The Half-Life 10th Anniversary Ultimate Strategy Guide (PC version)
This walkthrough is copyright 2008-2012 by Stanley E. Dunigan (email@example.com).
Always check one of the official host websites listed below for the latest version of this walkthrough.
GameFAQs (www.gamefaqs.com) -- always the first site updated
GameBoomers (www.gameboomers.com) -- official source of this RTF version
PlanetPhillip (www.planetphillip.com) -- official source of the PDF version
Cheat Happens (www.cheathappens.com)
Check the Universal Hint System (www.uhs-hints.com) for a complete Half-Life hint file. It's not a GameFAQs-style walkthrough, but instead organizes the hints into an HTML-like Q&A document, making it easier to find the hints you need without accidentally seeing other hints you don't want yet.
This is a very complete walkthrough of Half-Life that includes all of the best tips, strategies, and secrets that I've discovered or heard about during my thirteen or so years of playing the game. (I didn't get it until 1999, when it was on sale for $10 at CompUSA on the day after Thanksgiving. I got there late, and picked up the last copy they had!) I didn't keep track, but when I first wrote this walkthrough, I estimated that I'd played through the game more than 50 times. I figured that more than qualified me to write the ultimate, most super-detailed walkthrough ever for it. And what better time to do it than on the 10th anniversary of its original release?
This walkthrough was written with a conservative play style in mind, meaning that very few areas are skipped, and keeping your character healthy is always the main concern. When deciding what strategies to include and recommend, my top priority was to take as little damage as possible (within reason). My secondary priority was to use as little ammo as possible, especially rare ammo. I do often recommend using more ammo than is absolutely necessary so as to avoid compromising the top priority. (I once played all the way through the game using nothing except the crowbar, pistol, and hornet gun. That was painful!)
My third priority was to skip nothing, except for a few areas that I deemed to be way more trouble than they're worth. For instance, any skippable area that has several enemies and only a health pack or two in it clearly isn't worth the damage you'd take and the ammo you'd expend to clear it out, especially if your health is at or near 100. Of course, some side areas that I recommend visiting may not be worthwhile for you, so you'll have to make your own decisions as you go. (And quicksave often!) Hopefully, I've written the walkthrough so that anyone can use it to improve their gameplay experience.
To write the first version of this walkthrough, I played through the game in its original version (184.108.40.206) and with the version 220.127.116.11 and 18.104.22.168 patches installed. More recently, I've played with the version 22.214.171.124 patch, and also the Source and non-Source versions of the game that are available on Steam. The only significant differences I found were in the Source version, and SRC notes have been added wherever such differences were noticed.
If you have a favorite Half-Life strategy or secret that isn't in this walkthrough yet, send me an email at the address listed above in the copyright section. If I like it enough to include it after I try it out, I'll add it to the walkthrough and give you credit for it.
VERSION 1.50 (10/2/2012) NOTES AND CREDITS
This version adds in several new tips and tricks that I learned about while reading through the PlanetPhillip.Com TREE event.
· Section c1a2b: Note for skipping section c1a2c.
· Section c1a3: Note for opening the silo door early.
· Section c1a4: Tip for letting the rail car throw you to the exit pipe.
· Section c1a4i: Tip for using a barnacle to get to a secret area.
· Section c2a1: Note for using tripmines to get over the concrete barricade.
· Section c2a1a: Now advise setting up to three tripmines before descending on the lift.
· Section c2a1 (again): Tip for getting to the coils' activation switch faster.
· Section c2a2b2: Info about a tripmine in the water with the bullsquid.
· Section c2a2h: Shortcut for launching the rocket.
· Section c3a1a: Info on secret side room near ichthyosaur tank.
· Section c4a2a: New gauss gun altfire strategy.
· Section c4a2b: Info on how to skip killing Gonarch.
· Several minor SRC note additions and updates, including putting all SRC notes in italics.
VERSION 1.45 (5/9/2012) NOTES AND CREDITS
This version adds in Harry's tip about a secret area with three armor batteries in section c2a2d. And just when I thought I'd found it all!
VERSION 1.4 (9/14/2011) NOTES AND CREDITS
This version adds in a bunch of notes on the differences you'll encounter if you play Steam's Source version of the game. To find them all, you can do a search for "SRC:" (w/o quotes). The most significant differences are:
· Slightly improved physics cause floating crates to sink under your weight, hanging crates to sway a bit when you land on them, etc.
· Trigger points for enemies to drop down or teleport in are often in slightly different locations.
· Many creatures (especially headcrabs) wander around more than they used to.
· Enemies have more freedom of movement during combat, and will enter some areas that they wouldn't before.
· Ranged enemies (like vortigaunts and marines) can attack from farther away.
· Marines won't throw grenades around indiscriminately when you're out of sight.
· Crossbow darts are pulled down by gravity, and hornets fired from the hornet gun are more random and a bit less useful for sneak-shooting.
· You can't use tripmines that you set as "stepping stones" anymore, though you can use ones that were pre-set.
VERSION 1.3 (9/30/2010) NOTES AND CREDITS
I played through the game again to try out a couple of user-submitted tips, and came up with several new things of my own along the way.
· Section c1a0c: George's tip about when the vort appears in the test chamber.
· Section c1a2 (again): Tip for killing a headcrab past a floor grating early.
· Section c1a2c: Tip for best spot for sneak-shooting bullsquid in meat locker.
· Section c1a3a: Optimized route through area to skip some tripmines and turrets.
· Section c1a4d (again): Improved tips for fuel room combats.
· Section c1a4i (again): Tip for taking less damage when dropping down.
· Section c1a4f: Tip for ignoring bullsquid in lift room (based on a tip from Tony Sinclair) & new way to kill zombie next to reactor chamber.
· Section c2a3d: Improved crate-bashing tips for vort hallway.
· Section c2a5: New tips for fighting marines near dam.
· Section c2a5f: Improved tips for dealing with snark-infested vent shaft.
· A few other minor fix-ups and rewordings.
VERSION 1.26 (1/8/2010) NOTES AND CREDITS
This version mainly updates the email address in the copyright section (the wmconnect.com address is no longer active), though it also includes a few minor formatting improvements and other corrections.
VERSION 1.25 (4/5/2009) NOTES AND CREDITS
I played through the 126.96.36.199 game version yet again, and carefully reproofed the entire file, fixing errors and making minor improvements. No one's written in with anything, and I probably won't ever be able to find any more new tips, so this is likely to be the last release of this walkthrough.
VERSION 1.2 (10/11/2008) NOTES AND CREDITS
I played through the 188.8.131.52 game version again and came up with various new things, including:
· Section c1a1b: Another way to safely shoot the explosives past a ladder.
· Section c1a4: Easier way to kill the first bullsquid.
· Section c1a4i: Better way to handle firing chamber entry.
· Section c2a3a: Slightly better way to get the crossbow.
· Section c2a4e: Helpful notes for the lobby combat.
· Section c2a5w: Sneaky way to take down the marines.
· Section c2a5b: Way to make the rocket-firing tank blow itself up.
· Section c3a2c: Note about one teleport-in alien grunt not appearing.
· Section c4a1a: Great new shortcut.
· A few little misc. changes.
VERSION 1.1 (9/28/2008) NOTES AND CREDITS
For this version, I replayed the game with the 184.108.40.206 patch version installed. I didn't find anything new, but I re-proofed the entire walkthrough and made quite a few minor adjustments and clarifications. I also added brief descriptive names to each chapter section's title to help you more quickly figure out which one you're in, and I added several sites to the official host website list in the copyright section.
VERSION 1.0 (9/10/2008) NOTES AND CREDITS
This is the original version of this walkthrough, so I have no one else to credit yet.
STARTING TIPS AND NOTES
This walkthrough is organized around the same major chapter divisions that the game is, with these starting tips and notes put in at the beginning. If you're "joining us with a game already in progress," so to speak, you'll need to search for the title of the chapter that you're in.
Each chapter's info is divided up into sections that correspond to the chunks that the game itself is divided into. Whenever you move from one section to another, you'll see the word "LOADING..." in the middle of the screen while the section you're moving into loads up. Each section has an internal codename, and I use that in naming the sections in this walkthrough so that if you're on the PC, you can use the console's "status" command to see what section you're in (check the "map" field). Each section name also has some brief descriptive text in case you'd rather figure out what section you're in that way.
SRC: You can enable the console by going to the Options menu's "Keyboard" tab, clicking on the "Advanced..." button, and then clicking on the box next to "Enable developer console (~)." Note that you won't need to use the "status" command, since the current map code is displayed in the top right corner of the screen whenever the console window is up.
In many places in this walkthrough, I refer to the quicksave and quickrestore keys. If you're not already intimately familiar with them, get that way at once! To find out (and/or change) what keys are defined for those functions, go to the game's main menu and choose "Configuration" and then "Controls." (SRC: Go to the Options menu and click on the "Keyboard" tab.) I strongly advise you to redefine quicksave to be F5 and quickrestore to be F8 or F9. That way, the two keys won't be too close together. (That's practically an industry standard by now, anyway.)
Another thing you should do on the main menu's configuration screen is choose "Video" and then "Video Options," and move the gamma slider all the way to the right. (SRC: Go to the Options menu's "Video" tab, then click on the "Adjust brightness levels..." button and move the slider all the way to the left.) That'll make all the game areas much easier to see in, and it won't blind you or wash out all the colors like some games' full-gamma settings do.
I don't include anything about the Hazard Course (SRC: Training Room) in these hints, but you should start out by playing through it at least once, especially if you're not yet familiar with the concepts of jump-crouching (which the game calls "duck jumping") and crouch-jumping. Those moves are essential in many places throughout the game. I remember having a heck of a time on my earliest playthrus because I didn't know how to jump-crouch, and therefore had to use the "noclip" cheat to get past all the obstacles that you're supposed to jump-crouch onto.
I mention crouch-walking a lot in this walkthrough, but what I'm usually referring to is crouch-running, meaning you're moving around while using the "Duck" key, but not the "Walk" key. True crouch-walking involves using the "Duck" and "Walk" keys at the same time, and makes you move extremely slowly. This is sometimes useful, but usually not necessary. You can take any reference to crouch-walking to really mean crouch-running unless I say to very slowly or very carefully crouch-walk, in which case true crouch-walking should probably be used.
A favorite tactic of mine that I'll often say to use is sneak-shooting. That's when you sneak up on an enemy who's unaware of your presence and position yourself so that you can see only a small part of him, such as an arm or a leg. When you shoot that part, the enemy will often just turn in place to face you. If he still can't see you due to an obstruction to his view, you can keep sneak-shooting exposed parts until he's dead. Some enemies will move around a bit when sneak-shot, but they still won't be aware of you unless they get a clear look at you while moving around. If you're afraid that will happen, quickly strafe to where you'll be out of sight right after taking a sneaky shot. Once you get the hornet gun in the "Surface Tension" chapter, you can often use it to sneak-shoot enemies around corners, and even through ceilings and the bottoms of walkways, without having to see any part of them at all.
There's a peculiar glitch that might cause you to be frozen in place after you ride on a lift or elevator. When it happens, you may or may not start slowly taking damage. In any case, crouch and start moving around in order to break out of the glitch. If you're already crouched when the glitch happens, there won't be any way to break out of it, so don't ever crouch on lifts while they're moving. Unless you briefly crouch and then stand up again before the lift stops. That may help prevent the glitch in some cases. Jumping around right before the lift stops may also help. (SRC: This glitch never happens.)
One fun thing you could do to extend gameplay is to use the crowbar to beat on all the dead bodies you find (and make) until they splattify. I've always enjoyed doing that immensely, and I'll never forgive Half-Life 2 for making dead bodies invincible. (SRC: Dead bodies are invincible in this game, too. Dang it!)
BLACK MESA INBOUND
Sections c0a0 thru c0a0d: RIDING TO WORK
This is just the long, scenic tram ride that you have to go through every time you start a new game. You don't need to do anything during the ride, and could just go take a break until it's over, but you might want to check out the sights along the way.
To start with, you'll see a security guard on a little platform pounding on a door. That'll be you pounding on that door soon after you start playing the Blue Shift add-on game (though hopefully you won't look nearly as goofy as this guy does). You'll go through several areas past that, some of which you'll be seeing again as you pass through them on foot in the Opposing Force add-on game. Near the end of the ride, your car will stop briefly next to another one in which you'll see the so-called "G-Man," who I've nicknamed "Briefcase Bastard." He's always carrying that briefcase, and he's such a ... you know!
Section c0a0e: BEING LET IN
After the tram reaches the end of the line and stops, wait for the security guard to come over and open the door for you. Exit the tram and follow him over to a big reinforced door that he'll also open for you. Go through it and walk up to the second big door, then wait for the "Anomalous Materials" chapter to start.
Section c1a0: STARTING FUN
Go through the door and up to the desk with the security guard seated at it. After he finishes talking to you, look down at the desk and hit the "Use item" key in order to press a hidden button and sound an alarm briefly. (SRC: You'll have to go around to the other side of the desk to press the button.) That and using the communications console in the corner to the left are good for a few laughs. When you're done there, start down the big corridor with the large colored stripes on the walls.
After you turn a corner, you can check out a computer room to the left, and then follow the brown wall stripe past a couple of rooms and to a guarded door. You can have fun trying to listen in on the G-Man's conversation with a scientist or by turning off the lights in the other room, but what you need to do is return to the corridor junction and go toward the small downramp to get to section c1a0d.
Section c1a0d: GET YOUR HEV ON
Turn right past the ramp and follow the green wall stripe to the break room. Walk up to the microwave oven and press the "Use item" key repeatedly while facing it. You should soon be able to cause the microwave casserole inside to explode! (Note that this bit of hilarity will earn you a reproachful comment from Dr. Magnusson near the end of Half-Life 2: Episode Two.)
Leave the break room and continue following the green wall stripe to reach the employee locker room. The bathroom in the back right corner of the locker room isn't very interesting, but the HEV suit room in the back left corner is. Use its control panel to open up the one case that still has a suit in it, then walk into the case in order to put the suit on. Now you're ready to do some half-lifing!
Find the locker labeled "Freeman" near the bathroom entrance and push against its door to open it up. Go inside the locker to pick up an armor battery, then check out the wall-mounted first aid station just around the corner. You don't need any aid yet, but you're going to have to get used to the stupid "hee-yee-hee-yee" sound that first aid stations make when you use them, and now's a good time to get in some practice. (SRC: First aid stations won't make that sound if your health is 100.)
Go back the way you came, then go down the corridor with the blue wall stripe until you reach the security post. The guard will see that you've got your HEV on, and will open up the nearby security door for you. Go through it and the next door to get section c1a0a to load.
Section c1a0a: MOVING TOWARD THE TEST CHAMBER
Go around to where you can use a button panel to the left of some doors to open them, then get on the lift past the doors and use its button to descend to a lower level (or climb down the side ladder to reach the same area). Go through some doors and down a corridor, then keep going until you reach the spot where section c1a0b loads.
Section c1a0b: STILL MOVING TOWARD THE TEST CHAMBER
Enter the control room and wait while three scientists talk to you. After one of them uses a retinal scanner on the other side of the room, go through the door he unlocked and on to where two scientists (one of whom will supposedly be Dr. Eli Vance in Half-Life 2) notice some equipment problems. Across from them, use a button panel to summon a lift, then use its button panel to go up a level. Exit the lift and go down the corridor until you reach the test chamber door, where section c1a0e will load.
Section c1a0e: THE TEST CHAMBER
Enter the test chamber's outer room and wait for the two scientists to finish talking and open the main test chamber doors for you. Go through them and across to the other side of the chamber, where you'll be able to go up a small ramp. Look for a ladder on the wall past that, and climb it to reach an upper walkway. Go over to the walkway's computer panel and watch for the red glass cover on the button to rise. When it does, use the button, then watch as the big scanning machine powers up.
Climb back down the ladder and go stand next to the cage that's near the ramp's bottom. When the "specimen" arrives, do a quicksave, then get behind the gadget it's mounted on and push it forward into the scanning beam. Move back a bit after the crystal enters the beam and wait while you're teleported to a couple of harmless border world locations, followed by the "Unforeseen Consequences" chapter.
Section c1a0c: LEAVING THE TEST CHAMBER AREA
The first thing to do is check to see if a vortigaunt is in the test chamber ruins with you. This only happens very rarely, and when it does, you'll want to restore your quicksave and go through the telezapping stuff again in hopes that the vortigaunt won't be there next time. (Note that the vort will almost certainly appear if you pull the specimen's mounting gadget back out of the scanning beam after pushing it in, so don't ever do that.)
Leave the test chamber through the big jammed-open doors, then try using the retinal scan device that's next to the exit door. After the door opens, go through it to find a scientist trying to revive a security guard. You could wait around and take the guard with you (by talking to him after he's on his feet), but that's not helpful since he can't get over some nearby rubble.
Go around the corner and move forward slowly. After a computer bank falls over, go past it and jump over the debris that's in the corridor leading to the lift. It'll still work, so get in it and use its button. Go through the doors and over to the two scientists nearby. After they're through talking, get the black one (Dr. Vance, I presume) to follow you over to the control room door's retinal scanner.
After he opens the door, move far enough through it to get a large electrical surge to shoot into the control room through the window that's over to the right. Wait until the surge blows up the door at the other end of the room, then carefully time your run across the room so you won't get zapped. In the next hallway, section c1a1 will load.
Section c1a1: YOUR FIRST TWO WEAPONS
When you reach the next room, run through it and out its other door as quickly as you can, since a headcrab will teleport in right after you enter the room, and you have nothing to kill it with yet. In the next hallway, carefully crouch-walk under the red laser beam and over to where another laser beam will break free of its confining pipe. Don't try to crouch-walk under this one, but instead run around it right after it slices through a dead security guard's body.
Pick up the crowbar that's next to the nearby doors, then go back past the two laser beams and to the room where the headcrab teleported in earlier. Quicksave before entering the room, then check to see if the headcrab is levitating up in the air. If it is, you'll need to go around the large fallen pillar and toward the headcrab, right-strafing at the last instant to dodge its leap. Quickly turn and run up to it, then crouch down and crowbar-whack it before it can turn and leap again.
If the crab starts out on the floor next to the other end of the pillar, you can do the same dodge-the-leap thing, or you can let it see you, then crouch and back up around your end of the pillar so it can't leap at you. When it walks into view in front of you, quickly move forward and crowbar-whack it to death. (SRC: The headcrab may have its back turned to you, allowing you to sneak up on it.)
Move on until section c1a0c loads back up, then time your run through the control room again. (Note that it's best to wait for the surge to hit the spot that's farthest from you, then quickly run through.) Go all the way back to the test chamber door, then quickly crowbar-whack the revived security guard to death. After you do, you can take his pistol. It'll come in real handy soon.
Go all the way back to where you picked up the crowbar, then crouch down and use it to bash out one of the doors' lower glass panels so you can crouch-walk through. Do the same with the next set of doors, and watch the elevator crash. Turn right and climb down the ladder so you can grab an armor battery from the floor next to the elevator wreck. Climb back up that ladder, then climb up the ladder that leads up to the next floor.
Quickly get off the ladder and run through the doorway to find a zombie closing in on a nearby security guard. You want the guard to survive the attack, which he may not be able to do on his own. That's the main reason I had you go all the way back to the test chamber to get that other guard's pistol. Use it to quickly head-shot the zombie before it can kill this guard. (Or if the zombie notices you and starts coming toward you, back away from it while the guard shoots it for you.)
Hopefully, the guard will be able to shoot down the other nearby zombie all by himself, so you can just stay out of the way and watch. After that's done, talk to the guard to get him to follow you, then go through the nearby open doors to reach section c1a1a.
Section c1a1a: LOCKER ROOM REVISITED
Past the next set of doors, go around the corners just far enough to get your guard pal to notice two zombies ahead, then stay out of the way while he shoots them down. He won't notice the nearby dead scientist with a live headcrab on his head, so either ignore that or whack it to death with your crowbar.
At the path split, go straight ahead to find the corridor with the break room and employee locker room that you visited before. All you can do in the break room now is have fun vandalizing the soda machines with your crowbar. In the locker room, get two armor batteries from the "Freeman" locker, then grab the two bullet clips in the flapping-open "Guthrie" locker. Go back the way you came, then turn left and go up the slanty bit of floor to reach the spot where section c1a1f loads.
Section c1a1f: GETTING TO THE FORMERLY RESTRICTED AIRLOCK
Turn left and follow the hall to get back to the room you first entered at the beginning of the previous chapter. Notice the explosion that destroys a vent covering near the floor. Shut off the annoying alarm by using the security desk's button, then go over to the wall hole where the destroyed vent covering was.
If you can get the attention of the headcrab that you can see a short way past the wall hole, back off so your guard pal will shoot it for you. Otherwise, slowly crouch-walk toward the crab until it's crushed by a falling computer bank. Stand up and look to the left to see a second headcrab in the distance. You can either shoot it to death or try to lure it out to where your guard pal will shoot it for you. Either way, this is the end of the line for the guard, so crowbar-whack him to get his pistol.
Before you reenter the computer room, go over to the big doors that lead to the tram arrival platform. You can partly open those doors by crowbar-bashing the largest of the three panels on the wall to the right of the doors. Crouch-walk under the upper door, then run down to the other set of doors and do the same thing. You can then grab a bullet clip from near a dead guard, and you can kill a scientist by walking a short distance onto his unsteady bit of walkway, then quickly retreating before it collapses.
Go back through the two half-open door sets and then crouch-walk through the wall hole to get back into the computer room. Go to the room's back left corner and jump onto the slanty computer bank (SRC: You'll have to use a jump-crouch here), then crouch-walk through the small crawlspace to where you can drop down into a corridor. Watch the scientist in a nearby room get headcrabbed, and carefully avoid the same fate by not going near the section of fallen vent shaft that's just to the left of that room's windows.
In the dark room across the hall, you can whack a chair zombie to death and smash a few things. Past that, you'll come to an area where a security guard and a zombie are both about to die. If you're quick, you can crowbar-whack one of them a few times before they both turn intangible, but it's not useful. Grab the guard's gun and crouch-walk through the left part of the first set of doors to reach section c1a1b. (SRC: You'll probably have to do a crouch-jump to get through the doors.)
Section c1a1b: HOUNDEYES AND HAND GRENADES
Use the button panel on the left to get one of the doors ahead of you to start opening and closing. Time your way through it so it doesn't close on you and damage you. Turn right past the door and move forward with the crowbar ready. When a houndeye teleports in, back up a bit, then charge him and whack him with the crowbar as soon as he starts whining up a sonic charge. Do the same to the other nearby houndeye who's attacking a scientist. (It's perfectly fine if the scientist gets slushed.)
Move on to the next area, where you'll find two more houndeyes. You can either crowbar them to death or use the pistol to make sure you don't get zapped. If you jump into the side room that one of the houndeyes broke out of, you'll find a first aid station on one wall. Back in the main room, find a door in one corner with a headcrab past it. Open the door and immediately retreat, then carefully move to where you can shoot the headcrab without it hitting you.
When you come to a ladder, get the pistol out and slowly climb the ladder to where you can shoot the top of some large explosive containers, thereby blowing them up and destroying the zombie and headcrabs near them. It can be kind of tricky to climb the ladder just enough to shoot the explosives without getting damaged by the explosions or leaped at by the headcrabs, so you'll probably want to quicksave before you try it.
Or you could go back to the door you came in through and look near it for three metal barrels. One of them can be pushed and pulled around (SRC: All three of them can), so shove it over to the area with the ladder. Push it up against the wall that's directly opposite the ladder, then jump-crouch onto it. Stand and face the ladder, and you should easily be able to shoot the explosives without getting hurt. (SRC: If you take too long getting your barrel into position or jumping onto it, one or more headcrabs may escape the explosion and go after the nearby scientist. Also, you have to shoot the explosives twice to get them to explode.)
Go along the walkway past the top of the ladder until you come to a dead-end area where a zombie is passing his hands over a dead scientist in some bizarre alien ritual. Look near your end of that area to see if there's a large explosive device there. There may or may not be, depending on whether or not it was accidentally detonated by houndeyes earlier.
If it isn't there, you'll want to use the pistol to head-shot the zombie to death. If it is there, move close enough to the zombie to get its attention, then retreat past the explosive to where you can just barely see it around the corner. Shoot it quickly with the pistol (SRC: You'll have to shoot it twice) when the zombie gets close to it. Hopefully, the explosion won't damage you any. (Run backwards right after firing the shot to be sure.)
Return to the top of the ladder and go left to find a scientist sitting in a small niche area. Walk up to him to get him to stand up, then talk to him and have him follow you back to where you found the zombie. When you pass the retinal scanner, the scientist will use it to unlock the nearby door, which allows you access to a room with a first aid station, some hand grenades, and some bullet clips. Grab those goodies, then return to the houndeye room. (You can shortcut your trip back there by jumping over a railing.)
In the short corridor that leads onwards from the houndeye room, push one of the movable barrels as close to the door ahead as you can. Move around either side of the barrel until you hear a teleporting sound, then get back behind the barrel. Right after the vortigaunt breaks through the door, toss a grenade so that it goes into the vort's room. After it's blown up, enter its room to find some more bullet clips. (SRC: When you exit the room, look down the hall to the left to see if a headcrab is coming after you. Quickly shoot it to death if it is.)
Just past that, watch under the blue D475-KL sign for a zombie to climb up through a grating. You could shoot or grenade it to death, but there's no need to. (SRC: Go ahead and do it.) Stand back and toss a grenade so that it goes down the hole in the floor that's on your side of the bars. It should blow up the headcrab that's in the water directly below the hole. (SRC: There's no headcrab down there.) Toss a couple more grenades down the hole if you want to be sure the headcrab is dead, then go back to the room where you found the grenades. Resupply using the ones you couldn't take before, then return to the floor hole and drop down through it.
Explore the watery tunnel area until you find a small cement platform with a valve wheel on it. Jump onto the platform and use the wheel to flood the place, then swim over to the nearest ceiling grate. It'll open when the water reaches it, and you can hop up through it. The zombie that climbed through another grate will be nearby, but you can ignore it and go down the hall to where section c1a1c loads.
Section c1a1c: CANAL AREA
You'll soon come to a big room with a large platform lift in it. On the walkway next to the platform, get the two bullet clips that are near the dead security guard. You're now supposed to hit the big lever to get the platform moving, then ride it down, dodging headcrabs as best you can. However, a much better way is to ignore the lever and drop from the right side of the unmoving platform to the slanty slope underneath it, then hold down the "Move right (strafe)" key as you slide down. You should end up on a narrow ledge next to a first aid station without taking any damage.
SRC: Hit the lever to start the lift, then quickly get onto it and strafe right so that you land on a narrow gray metal ledge. (It is possible to get onto that ledge without starting the lift, but it's very hard.) As soon as you're on the ledge, lean on the "Move right (strafe)" key to make sure you stay on it, and use the "Move back" key periodically to slow your descent so you won't hit the first aid station's ledge hard enough to take damage.
Jump across to the main floor using the four raised cement things next to the aid station, then quickly shoot the houndeye that teleports in on top of a large crate. When it falls down into the crate, move around to where you can shoot it through a crack in the crate's side. (Or just bash through the crate with the crowbar and whack the houndeye to death.) Bash all of the crates to find more bullets before you move down the adjoining corridor.
When you come to a room with a metal walkway crossing it, strafe left to avoid the bullsquid's toxic spit when it teleports in and falls. Go a short way onto the remaining metal walkway piece, then turn right and jump to the lowest set of nearby pipes. After jumping onto the highest pipe, move down to where you can jump onto a large machine and crawl along another pipe. Jump to the highest pipe past it, then follow it along to a small platform with a vent grating. Bash the grating with the crowbar, then crouch-walk through the vent shaft until you reach the second floor grating at its other end.
Bash it and drop through, then turn right and bash all the crates you find to get armor batteries. Look across to the lower floor on the opposite side of the big room ahead to see a bullsquid killing off several headcrabs. As soon as it's done with that, use your pistol to kill it, strafing whenever you need to in order to avoid its spit. Note that it may not have seen the leftmost headcrab due to a crate blocking its view, so shoot that headcrab, too. (SRC: Don't kill the bullsquid yet.)
You now need to cross over to where that bullsquid is. The fastest way is to use the broken piece of metal walkway that's near you. Take a running jump off the left end of the walkway piece, and you should make it across, though you will take some damage. Note that if you do this while the bullsquid is still killing headcrabs, you can run for the nearby door and avoid having to shoot anything.
A much safer way is to go back the way you came to find a door you can go through, past which is a ladder you can climb down and another door you can go through. (SRC: Stand behind a nearby barrel and wait until the bullsquid kills the new headcrab batch, then shoot it, crouching for cover when it spits at you.) You can push a wooden crate into the canal and use it to jump across, but be quick, or it'll float away. (SRC: Crates will sink under your weight, so you can't use them to get across.) Or you can enter the canal, hop onto one of the little lights that are spaced along its other side, then jump-crouch onto the floor. Or you can swim to the canal's other end, use a short ladder to climb to a small room with a first aid station, then go through a door and along a narrow ledge.
In any case, go through the door near the bullsquid and down a corridor to reach section c1a1d.
Section c1a1d: BOX-HOPPING FUN
Keep going until you reach a large room with hanging crates and two ladders. After you climb the second ladder, quicksave in case you fall, then jump onto the railing next to the rightmost of the two nearest hanging crates. From there, you can move forward onto the crate, then do a running jump to reach the next crate that's directly ahead. (SRC: The crates will sway a bit when you land on them, making it a bit trickier to jump or drop from one to the next.) Drop down to the next crate without jumping, then turn right and drop down to the next two crates in order. Then you can finally drop onto the floor past them. Move down the corridor until you find a ladder to climb in a red-lit room. Past it is a corridor that'll lead you back to section c1a1c.
Section c1a1c (again): EXIT ELEVATOR
Move down the corridor until you exit it through a door, then go right to find a big elevator that you can open with a button panel. Enter the elevator and use its interior button panel to ride to the "Office Complex" chapter.
Section c1a2: HALLWAY ELECTRICAL HAZARD
Leave the elevator to find a health pack and armor battery, then turn left and watch as an electrical hazard kills several headcrabs. None of them should make it to you, but have your pistol ready just in case. You could get past the electrical hazard quickly by running down the left side of the hall, but you'll take a lot of damage, and there's a much better way.
Find the vent grating in the wall near the electical hazard and crouch-walk carefully up to it. Bash it with the crowbar (SRC: It gets destroyed by the explosion), then enter the vent shaft and turn left. When you come to a barred window that looks into a fan room, turn right and use your flashlight to help you find your way to a grating. Bash it, then move around in the shaft until all the headcrabs in the fan room get killed by the fan.
Don't enter the fan room yet. Go back the way you came until you reach the other end of the vent shaft. After bashing through another grating, you'll be able to drop down to the floor and open the two nearby locked doors from the inside. You can also bash the two vending machines and have fun crunching all the bugs that come pouring out of them.
Approach the scientist near the table lamp to get him to say that if he'd known it was you, he'd have let you in. Oh, really? Talk to him to get him to follow you, then maneuver him into getting caught by one of the three barnacles in the area. That'll learn 'im! You can then have fun killing the barnacles by letting them catch you, then bashing them with the crowbar when they pull you in close.
Find the door with the high voltage sign to the right of it, then go through it and use the lever on the panel to the left. That'll turn off the power to several nearby devices, including the hallway hazard. Return to the vent opening in the hallway and reenter it, going left to return to the fan room entrance. Drop into the fan room and check near the dead security guard for two bullet clips.
Crouch-jump back into the shaft, then return to the hallway and go past the now-deactivated electrical hazard. The door past it won't open, so bash the glass out of the window and crouch-jump through it. Pass by the D-AL 101 room for now, and move up against the unopenable wooden door in the small side area marked "STORAGE." Wait until a zombie breaks completely through the wooden door, then quickly shoot it to death.
In the dark storage room, crouch down and move around on the lowest part of the wrecked shelves until you're able to pick up both bullet clips. Find the dim corridor past the storage area that's clogged with wooden crates, then bash crates and run over orange scuttlebugs until you reach the point where section c1a2d loads.
Section c1a2d: SHOTGUN AND SECURITY CAGE
Bash every wooden crate except for the very biggest one. There's a headcrab on its other side, and you'll want to very slowly crouch-walk past the crate until you're in position to sneak-shoot the headcrab. (SRC: The headcrab may crawl over to where the guard in the cage will shoot it.) After that, bash the crate and move on to where you can turn a corner and find a shotgun and some shells on a green crate. (Note that you'll probably have to jump onto the crate in order to pick up everything that's on it. The same will go for other green crates you come across.)
As you approach the caged-in area with a security guard in it, a zombie will walk into view. Shoot it once with the pistol to get it to focus on you, then let the security guard finish it off and open the gate. (SRC: There's nothing you can do to distract the zombie, so run up to the gate and quickly kill it with the shotgun.) Before you enter the cage, drop down to the lower floor and bash crates to find a health pack and an armor battery. Climb the ladder to the higher floor, then go through the gate and grab the ammo from the green crate near the guard.
Talk to the guard to get him to follow you, then go down the short hall to the room past the cage area. There's a headcrab in an overhead vent shaft, so run to the back of the room to get it to leap at you, then quickly back up and strafe aside so it'll miss you and get shot by your guard pal. Get all the ammo in the room, then go back through the cage gate and on to where section c1a2 will load up again.
Section c1a2 (again): ELECTRIFIED ROOM AND AUTOTURRET
Lead your guard over to the D-AL 101 room's big broken window so he'll shoot the headcrab in the room for you. Talk to him to leave him where he is, then crouch-jump onto the window's sill. Pull the nearby table toward you by facing it, holding down the "Use item" key, and moving backward. Once it's next to the window, get back on the sill if you fell off and crouch-walk onto the table.
SRC: Bash the pieces of glass out of the sill, then hop onto it and drop into the water. Quickly crouch-jump onto the table before you take very much damage. It is possible to crouch-jump onto the sill and then onto the table right away without touching the water, but it's fairly hard to do.
Jump from the table to the large counter on the right, then jump over the sink in the middle of the counter (its water is electrified, too). Jump from the end of the counter to the small table that's next to the first aid station, then jump to the small counter that the dead headcrab is on. Use the light switch on the wall to turn off the electricity, making the room safe to move around in.
Find the vent shaft in the wall a bit to the left of the light switch counter and stand in front of it with your flashlight on. There are three headcrabs in the shaft, and the easiest way to kill them is to wait for them to approach the grating and shoot them through it. (SRC: They may not all approach the grating. In fact, some may crawl on down the shaft.) After you kill all three of them, you can bash off the grating and crouch-jump into the shaft. But first, go over to the big cabinet in the corner to the right of the first aid station, nudge its door open, and go inside it for an armor battery.
Move along the shaft, being sure to stay crouched as you go under a large fan. You can wait and watch as headcrabs drop into the fan and get splattered, or you can just move on without stopping. When you reach a grating, bash through it and move forward to fall down into a hallway past some doors you couldn't open earlier. Open them both now and get your guard following you again, then move down the hallway and take cover behind a large metal crate while the guard shoots some drop-down headcrabs for you.
After the crabs are dead, tell your guard to wait for you again, then push the small metal box to where it's directly underneath the broken-off ladder that you can see up in the ceiling area that the crabs dropped down from. Get onto the box so you can jump from it to the ladder. (SRC: You'll have to push the big box to a spot under the ladder, then use the small box to crouch-jump onto the big box.) Climb the ladder and move over to a large bashable grating in the floor. Bash it with the crowbar, then get the pistol out so you can shoot the headcrab that's ahead as soon as you drop down. (You could instead use the flashlight to find the headcrab right after getting off of the ladder so you can shoot it before bashing the grating.)
Turn around and bash out the wall grating, but don't drop through it into the next room yet. Move far enough forward to get the noisy autoturret over to the right to power up, then quickly back up before it can shoot you. After it shoots a scientist and a headcrab, wait until you hear it power down, then quicksave.
You could drop into the room and run straight forward to the headcrab-infested hallway and move on from there, but that would mean skipping some good stuff. As soon as you drop to the floor, turn right and run up to the leftmost wooden crate. Crouch down and push the crate forward as far as you can, then bash it to get it out of your way. You can then use the switch on the metal control box to turn off the autoturret.
Grab the bullet clip from the middle of the room, then go through the red-outline doorway that's to the left of a dead scientist. Check the green crate and set of shelves back there for ammo, then find the red door that you can push open to return to the hallway where you left your guard. Get him to follow you again, then push and/or pull the small metal box all the way to the turret room. You can use it to get onto the large metal box near the turret's platform, then jump to the platform to access a first aid station.
Help your guard kill off all the headcrabs in the hallway that leads off from the turret room, making sure he doesn't take very many hits. Past that, start up some stairs to reach section c1a2a.
Section c1a2a: VORTIGAUNT OFFICE AREA
Go to the top of the steps to find a second guard shooting headcrabs. After he's done with that, talk to him to get him to join you, giving you a total of two guard followers. You'll need 'em! Bash the nearest crate to find a bullet clip, then approach the large red-rimmed doorway cautiously. A headcrab will drop down through a weak ceiling panel as you go through the doorway, so quickly back up and let your guards shoot it for you.
Talk to them to leave them behind, out of sight of the hallway. Go partway down the hallway to find a side room to the left that you can get an armor battery and health pack from. In the hall, turn and face toward the flashing green EXIT sign, then slowly back up until some nearby vortigaunts see you. Quickly run forward and into the side room, then squeeze into the space behind the open door. Neither you nor the gaunts can shoot through any part of the door, so watch for them to try to come behind the door after you, and double-barrel them with the shotgun when they do. (SRC: Crouch down to make sure the vorts can't whack you through the door with their melee attacks. You may also have to go out several times to lure more in.)
After they're all dead, go back and get your two security guards following you again. Go past the side room to the intersection area, then look to the left for a weak ceiling panel. Move toward it, then quickly retreat when a headcrab falls through. After your guards shoot it for you, go to the lounge-like room ahead and repeat the process with its ceiling-hid headcrab.
Look through the lounge room's small doorway to see a vortigaunt who thinks it's hiding in a dark corner. Shoot it once with the pistol, then retreat and let your guards finish it off. Around the corner from there is a small side office with a vortigaunt in it. Let it blast its way through the office window, then go in and get some bullets from the desk after your guards kill the vort.
From there, go down the hall to a well-lit area with two doors, one of which is labeled D-AL 102. See if there are any vortigaunts near that door or in the room past it, then lure out the ceiling headcrab in the other room for your guards to shoot. There's a first aid station in that room if you need to heal up. In the D-AL 102 room is another door with that same label guarded by a barnacle. Crowbar-whack it, then enter the scientist's dark room to find a health pack on a desk. You can turn the room's lights back on using the wall switch near the scientist if you want to be able to see better.
Return to the lounge and hop up onto the couch right in front of the "Maintenance Access" sign. Look up and bash the weak ceiling tiles, then climb up the ladder past them. Look into the autoturret's alcove to get it to notice you and activate, then quickly duck out of sight and use the switch on the metal control box to turn it off. Get the shotgun ammo from underneath it, then climb back down the ladder to the lounge.
Find the short exit corridor to the left of the lounge that has vending machines in it, then toss a hand grenade so that it blows up the vortigaunt that's hiding behind the farthest machine. Have the shotgun ready to blast a couple of other vorts in the area just past the vending machines. If you have any security guys left after that, you can either whack them for ammo or let them stay with you. I'll assume you don't have any left, so you don't have to worry about making sure they survive this area.
Kill the barnacle past the exit corridor with the crowbar, then go up the first set of stairs. Move up the second set very slowly and with your pistol out, since there are three headcrabs just past the top. Try to shoot all of them to death before they can leap at you, or just toss a grenade up there. In the next hallway is an explosive crate and a zombie. Wait until the zombie is passing by the crate, then blast it with the shotgun. If that doesn't finish the zombie off, give it a close-up head shot with the shotgun.
Move slowly toward the point where the corridor turns left, since there are two vortigaunts just around the corner. Get to where you can just barely see part of one, then lob a grenade so that it'll bounce toward the vort. If that doesn't kill both of them, round the corner and double-barrel the survivors. Move on past them to reach section c1a2b.
Section c1a2b: OPTIONAL AREAS AND ZOMBIE CAFETERIA
Stay on the left side of the hall while approaching the door so a headcrab on the vent shaft above the door won't see you. Go through the door to enter an area with a security guard, but don't have him join you yet. Instead, use the flashlight to locate a floor-level vent grating to the left of the door you just came in through. Bash the grating and move along the vent shaft until you reach a big fan room. Climb the ladder and go over to where the fan blades are turning. Time your run through them so that you're going across when the broken-off blade is on top.
Bash the floor grating past the fan, then drop down and move along until you come to a wall grating. Carefully shoot two headcrabs through the grating before bashing it, then bash through another grate past them. Walk along the top of a vent shaft in a hallway, looking for another grate to bash and go through. Past yet another grate is an open area with some rusty metal beams that you need to cross.
You can cross along the left side, carefully moving around the cable that's in the way, but it's a lot easier to go around the cable using the other beams. When you do, some headcrabs will break through a wall ahead and to the right. Quickly shoot any crabs that leap out, including ones that fall to the floor below, then toss a hand grenade into the crabs' wall niche to kill any others that are in there before you go past it.
Move carefully along the beams to where you can enter another vent shaft after bashing its grate. When you come to the end of the shaft, look into the room beyond to find a headcrab to shoot. Go around to where it is, then crouch-hop over some beams and walk on some weak ceiling tiles that'll drop you into a secret ammo room. After taking what you need, open the room's door and go left to get back to the place with the security guard.
It's still not time to get him to join up, though. Go down the large ramp near the guard and turn right. Don't approach the lower room with the crates and barrels yet. Stay well back and destroy the middle crate with the pistol. You'll then be able to safely sneak-shoot the bullsquid that's behind the crates. (SRC: Quicksave, then move as far back as you can and stay crouched while sneak-shooting the squid so he won't see you when he jumps up in surprise at being shot. If he does see you, quickrestore and try a different position.)
Go down there and loot the area of grenades and shells, then push the two barrels up to the yellow floor line so that they mostly block the path. Go a short distance past the yellow line to get two vorts to teleport in, then quickly get behind the barrels and shoot the vorts over them. (SRC: Watch out for them coming around the barrels to get you.)
Go back up the ramp and get the security guy to follow you, then go past the secret supply room's open door and on to a large cafeteria room where a zombie is messing around near some tables and dead bodies. Toss a hand grenade at the zombie, then help your security guy kill it and the headcrabs that fall into the room. (SRC: Have your guard pal stay at the top of the stairs. Go down them and forward a bit to get some of the headcrabs to drop down, then quickly retreat back up the stairs. After they're all dead, go toward the back of the room to get the rest to drop down, then quickly retreat again.) At the back of the room, use the crowbar to bash all the boards off the doorway, then go down the hallway until section c1a2c loads.
NOTE: You can skip section c1a2c by leading your guard down the short hallway to the left of the cafeteria that ends in a locked door. Get the guard close to the door, then nudge up against him until he moves up next to the door. Nudge him some more if necessary to get him to open the door (SRC: He won't ever open the door), then go through it to get to the area where you would've dropped down to the floor from a vent shaft if you'd gone through section c1a2c. (Note that the guard and zombie that would've been there on the long route will be missing. Also note that the zombie in the cafeteria can open that door for you, but it's more dangerous maneuvering it into position.)
Section c1a2c: MEAT LOCKER AND VENT SHAFTS
Around the corner is a room with two zombies feasting on dead scientists. Your dumb security guard will run right up to them and get himself whacked if you don't leave him behind before entering that room. Toss a grenade at the zombies and finish any survivors off with the shotgun, then go get your security guy to follow you again. (SRC: Go ahead and take the guard in with you, since he'll probably shoot the zombies while they come after you.)
Use the large lever that's to the left of the big door near the zombie area, then run through far enough that your security guy will follow you in before the door closes. If he doesn't make it, you can move up to the right side of the door and use the lever to open it (even though the lever is on the other side of the door). You could also do this if you want to return to previous areas for something. (SRC: This kind of "reach thru" glitch doesn't work.)
In the meat locker area's first room, go through the large open doors, then turn right. Let the headcrab around the corner see you, then retreat so your guard will shoot it for you. Bash your way past the hanging meat, then look through another large set of open doors to find another headcrab on the floor and one up on a high shelf to the left. Shoot them yourself or get your guard to do it.
After those two crabs are dead, go into the large room with three hanging pieces of meat. There's another headcrab nearby to shoot, plus a bullsquid hiding behind some crates a ways past that. Move onto the left end of the black-and-yellow strip in the big doorway, then turn on your flashlight and scan the crates until you see one of the squid's fat, slimy legs. Shoot the leg until the squid dies (your guard may help by shooting the squid when it jumps up), then move into its area and look for another headcrab nearby. (SRC: There's no black-and-yellow strip, you should stay crouched while shooting the squid, and you may want to leave your guard in a previous room while you do so.)
Find the big red-lit switch on the wall and use it, then move down the hallway and turn right to enter the back rooms. As soon as you do, a scientist will start running, chased by a bullsquid. Help your security guy take the squid down, then whack him for ammo. Look back in the room the squid started in to find some bullets and grenades on the floor next to some dead bodies.
Return to the starting room and climb up the short ladder to get onto a shelf. At the other end of the shelf, break the vent grating and jump-crouch into the vent shaft. Break out its other end, then follow the shelves along until you come to a spot where you can get on the moving platform. Do so when it passes by, then break its crates open for armor batteries. When it moves past the vent opening that's across from where you boarded it, quickly get off.
With your flashlight on, move down the vent shaft until you're near a spot where it drops down to a lower cross-shaft. A headcrab will jump up from the lower shaft as you approach, but it should miss you. After it does, carefully edge forward to where you can sneak-shoot it, then drop down and turn right at the shaft intersection to find an armor battery and a bullet clip near a dead security guard.
Turn around and go all the way to the other end of the shaft, then break the vent grating and enter a very shaft-y room that has several barnacles in it. Go around and crowbar-whack them and grab the supplies that are near them. When you're ready to move on, find the ladder that's near one of the barnacles, then either climb the ladder and drop onto the shaft to the left of it, or jump up to where you can kill the barnacle and go from there. At the top of the curving shafts, crouch-walk over to the large shaft opening and hop into it.
Move slowly along the dark shafts with your pistol out and your flashlight on, scanning ahead for headcrabs to shoot. Soon after you find one, you'll reach a spot where section c1a2b will load up again.
Section c1a2b (again): GOING UP THE ELEVATOR SHAFT
When you reach a grating, bash it off, but wait until the guard below shoots down a zombie before you drop down. (SRC: The zombie may kill the guard if you don't distract it by moving to the very edge of the shaft.) Walk up to the guard to get him to say something, then talk to him to get him to follow you. You can go through the door the scientist opened to get back to some previous areas, including the secret ammo room, if you want to. When you're ready, head up the stairs and get your guard to kill the headcrab at the top.
Walk down the wide corridor until a zombie drops down from a higher area. Stay back and let your guard kill it, then move forward until another zombie breaks through a wall and comes out to where your guard can shoot it. Go through the zombie's wall hole to find a dark area with some hand grenades, then crouch-jump through the office window that a scientist broke out through to find some shotgun ammo and health packs. Crouch-jump back through the window, then whack your security guy for his pistol clip if he's still alive.
Now you're going to have to ascend the shaft that's past the jammed-open elevator doors at the end of the hall. Quicksave, then take a running jump through those doors and across the shaft to the ladder that's on the wall. If you don't make it, quickrestore and try again. It's a pretty tough jump to make. Climb up the ladder and get off on the ledge to the right, climb up the next ladder and get off to the left, then climb the third ladder and get off to the right.
You're now on the highest ledge in the shaft, so you'll need to jump to the ladder that's on the side of the elevator car (after quicksaving). Climb onto the top of the elevator car, then look around on it for a bashable grate that you can drop in through. Move up against the elevator doors to get them to open and take you to the "We've Got Hostiles" chapter.
"WE'VE GOT HOSTILES"
Section c1a3: FLOOR TURRETS AND ASSAULT RIFLES
NOTE: You can skip this entire chapter by using a cheap trick. As soon as you exit the elevator, run over to the right and wait if necessary for a scientist to start pounding on the windows of a control room. Before he runs off, hit him once with the crowbar, then wait for him to run past the control room door. He should open it as he goes. To help ensure that he goes that way, get over on his left side before you hit him with the crowbar. If it works, you can enter the control room, use the big red button to open the nearby silo door, then go through it and move on to the "Blast Pit" chapter. (This trick works much better in the Source version of the game than in the original version. I guess that's to offset the cheap chapter-skipping trick for the "Power Up" chapter, which only works with the original game version.)
Watch as a scientist panics and runs into a laser tripmine at the end of the corridor, then use the nearby first aid and HEV wall stations if you need to. Go past the fire door, optionally bashing its button's glass cover as you go. When you reach the spot with two red laser alarms, run through them, then crouch down and move up against the right wall. That way, the floor turret won't be able to see you and shoot you.
Crouch-walk up to the corner to get a headcrab to teleport in over to the right, then back up while the turret blasts the crab for you. After the second headcrab appears and gets shot, crouch-walk up to the wooden crate that's ahead of you, then strafe slowly to the right until you can see one leg of the turret. Shoot it with the pistol until it falls over. (SRC: The second headcrab won't teleport in until after you move farther into the room.)
Get the Mp5 assault rifle that's near where the headcrabs teleported in, and immediately reload it since it only starts out with half a clip in it. Bash every non-explosive crate to find armor and shells, then go around to the other side of the fencing to get a headcrab to teleport in. Run back around the fence so you can shoot the headcrab through it, then wait for two more to teleport in for easy shooting. (SRC: You'll have to move around in the area past the fence to get the other headcrabs to teleport in, and there may be up to four more.)
Go through the fire door without bashing its button's glass and closing it, then jump over the first tripmine and crouch-walk under the second one. In the following corridor, move forward until a vortigaunt teleports in ahead, then quickly go all the way back to the fence that's past the fire door. If you wait there, two vortigaunts should kill themselves on the tripmines. If they don't, you'll have to go get their attention again (or just shoot them).
After two vorts are tripmine-killed, there'll be one more in the hallway, so go shoot it down with your new assault rifle. (SRC: There'll only be two vorts in all, and the second one won't appear until you get close to their teleport-in point.) Check the area the vorts teleported into to find a first aid station and two bullet clips next to a dead security guard. (SRC: No bullet clips.) Have fun vandalizing the soda machines and running over orange bugs if you want to, then head down the hallway and to the bottom of a large ramp.
Get your shotgun out and quicksave, then jump over the red laser alert beam, turn to face the two nearby explosive barrels, and blast them with the shotgun the instant a vortigaunt teleports in next to them. That'll kill the first one, and a good double-barrel blast will kill the second one that appears. Or if you'd rather skip that, you can jump over the laser alert's right end and immediately run to the right so that the first vort won't see you. If you carefully stay out of his sight, you can just leave him there, and he won't bother you.
It's fairly easy to sneak-shoot the two nearby turrets, but there's no need to. The ones you need to take out are on the other side of the big green crate stacks. After you bash the two large wooden crates that are next to each other, you'll be able to see one of the turrets past them. Move to where you can only see one leg of the turret, then shoot it with the pistol until it goes down. For the other turret, go around to the right side of the green crate stacks, bash the wooden crate there, then shoot the turret leg that you can see past it.
Hop up to the top of the biggest green crate stack. Note that you'll have to use a jump-crouch maneuver to get onto the uppermost crate. Once you're up there, drop down to the floor past the stacks, run through the fire door, and jump up onto the green crate stack past it. If you're fast enough, you can drop down into the next area, where section c1a3d loads, without any teleport-in headcrabs catching up to you.
Section c1a3d: MEET THE MARINES
Crouch-walk very carefully on the super-slick wet floor until you can see the nearest of the two turrets around the corner. Move to where you can only see one leg of it, then shoot it until it falls over. Repeat with the second turret, which is farther down, near the fire door's glass-covered button. You'll have to crouch-walk very slowly and carefully to get to where you can shoot it without being shot. (Or you can try tossing hand grenades so they bounce toward it, or you can try charging it with the shotgun as soon as the first turret goes down.)
After both turrets are down, check past the fire door to see if there are any unexploded tripmines along the left wall. If so, stand back and shoot the nearest one with the pistol. Go through the fire door to find a first aid station and several boxes to bash for supplies. Climb a ladder to reach a walkway that has more boxes to bash.
After going up another ladder, get your assault rifle out and move along the walkway until you can look down into a room with a marine in it. He's a hostile, so immediately open fire on him. You should be able to kill him before taking much if any fire. If you do get damaged, return to the previous room for health and armor.
Go down to the lower floor and look around for an aid station and some assault rifle clips on a green crate (and a rifle next to the dead marine). When you're ready to go, press the button to the left of the large lift to open it up. If you saved the scientist, he won't be of any use to you in the area ahead, but it can be fun to get him to follow you and then hit the lift's interior button to slam its doors shut on him! As you ride the lift up, section c1a3a will load.
Section c1a3a: MORE FLOOR TURRETS AND SEVERAL MARINE SQUADS
After the lift stops, stay back while a scientist runs forward and gets shot up by the three marines in the area ahead. Stay in the lift with the assault rifle out and shoot any marines you see running around on the upper walkway ahead, then find the dark passageway that's to the left as you exit the lift. Go back and forth in it, dodging grenades and shooting marines with the assault rifle when you can.
SRC: The marines will probably run into the side area with you, so it's not safe at all. Start by trying to kill the marine on the upper walkway with the pistol, then wait near the side area's entrance with the shotgun out for one to get near some explosive barrels. Blow them up, then go after any survivors with the assault rifle.
After all three of them are down, go all through the area and bash wooden crates to find supplies. If that's not enough to fully heal up, use the first aid and HEV stations near the back right corner of the area and/or take the lift back down to previous areas to collect leftover supplies. When you're ready to move on, find the stairs that lead to the upper walkway. Go through the fire door and along a wide bridge, watching out for barnacle tongues. If they're too hard to avoid, even when crouch-walking, look up and kill the barnacles with the assault rifle before passing under them.
You could use the barnacle whose tongue dangles closest to the bridge above you as a shortcut for getting up to it. Quicksave before you try, then while facing the bridge and looking up, let the barnacle grab you and pull you up. Hit it with the crowbar when you get within range, then lean on the "Move forward" key to land on the bridge. Turn left and go along to find yourself on a walkway above the room with the exit lift. The following paragraphs will assume you don't take this shortcut, so if you do, kill off the marines in the room below and then skip ahead to the last paragraph before section c1a3b starts.
Past the barnacle bridge, you'll reach a path split with two laser tripmines to the left. Ignore them and go down the ramp to the right to find a large area with crates, barnacles, and a fast-moving conveyor belt. There's also a higher floor that you can't get to that has lots of crates and several marines on it. Toss a few grenades onto that higher floor, then make sure the surviving marines see you. Go back up to the top of the hallway ramp to be safe, then wait while the marines toss grenades all over and eventually kill themselves. If you don't want to wait for that, stay crouched halfway down the ramp and shoot marines when they run into view, or go to the back of the lower floor area and jump up and down so you can see onto the higher floor better. (SRC: They're less likely to kill themselves with grenades and more likely to run around on the upper walkways, including the upper barnacle bridge.)
After all the marines up there are dead, you could go back and use the above-mentioned barnacle bridge shortcut. You'd be skipping some combat and supplies, but not a whole lot of either. If you'd rather not do that, jump onto the conveyor belt at a point past the barnacle tongues. Run along the belt to reach a room with some assault rifle clips near first aid and HEV wall stations. Find the lowest green crate in the big crate stack, then jump your way from it up to the highest green crate (using a jump-crouch or the big wooden crates to get onto it). Jump from there to the high-up conveyor belt, then run along it until you come to a room.
Quicksave while still a ways back from the room, then move into it far enough for the marine on its other side to see you. Quickly back up until you're near the bend in the conveyor, then wait for the marine to run over to a spot next to the explosive barrels you can see ahead. When he does, shoot the barrels to blow him up. If he blows up the barrels or damages you with a grenade (or magically replicates himself), quickrestore and try again. An alternative way is to blow up the barrels as you approach the room, throw a grenade toward the marine's sandbag wall before he sees you, then charge him while he's busy trying to dodge the blast.
Search his side of the room for a first aid station and some ammo, then look down to the lower floor to see several turrets and laser alarms. After quicksaving, drop down so that you land next to the fire door's button, then go through the fire door and jump over the laser tripmine. If anything goes wrong, quickrestore and try again.
Turn left past the tripmine and move forward a bit, then look up to see a marine's legs on an upper walkway ahead. Shoot his legs, then wait and see what he does. He should run around the walkways to some stairs that lead down to your floor. A barnacle has its tongue dangling right over those stairs, so the marine should get caught in the tongue and eaten. There are two other marines up there that you can trick into doing the same thing. However, if one of them tries to go down the stairs soon after the previous one is snagged, he'll make it past the barnacle, and you'll have to shoot him down. (SRC: The marines will probably kill the barnacle, so stay way back and try to kill them all with the pistol before they can get close to you. You may also want to use some grenades.)
Quickly run up the stairs while the last marine is keeping the barnacle busy (or kill it with the pistol before going up), then look for some shotgun shells on a small green crate near a sandbag wall. Go up some more stairs and run along the walkway until you reach a point where you can turn left and enter a wide concrete corridor. If you continue down the walkway past that point, you'll find a first aid station and some assault rifle clips past a hard-to-see barnacle.
Go down the concrete corridor and across another barnacle-tongue bridge, then on to where you'll find yourself on an upper walkway over an area where you've already killed off some marines. Go around the walkway and bash crates to find an armor battery, then locate the stairs that lead down to a lower walkway. It'll have some stairs that will take you to the floor the marines were on. Bash all the crates on that floor to get more stuff, then find the big "SURFACE ACCESS" lift in the back and use its button to open it up. Get on it and use its interior button to ascend to section c1a3b.
Section c1a3b: BRIEF SURFACE RUN
If the lift appears to jam as soon as this section finishes loading, crouch down and move around to break out of the glitch. After the lift stops at the top, crouch-hop onto the floor past it, then turn left and run for the corner with the first aid station on the wall. If you're careful to stay left as you run, you should make it without any of the marines outside seeing you.
After quicksaving, go through the left side of the large doorway, then immediately turn left and run past two sets of wooden crates. Turn right and run for the open door that's past another set of wooden crates. It might help to crouch as you drop down to the door, which is on a slightly lower bit of ground. As soon as you're through it, climb down the ladder that's past it to reach section c1a3c.
Section c1a3c: DROPPING DOWN A SHAFT
Finish climbing down the ladder, then quickly bash the crates in the area to find ammo and use the first aid and HEV stations to recharge. Move over to the vent access door to get it to open, then back up a bit as a big explosion sends debris down the shaft past the door.
There shouldn't be any marines alive in the shaft right after that, but there could be, so have the assault rifle out and ready. Quickly move through the vent access door and drop down to the ledge you see on the right, then turn and try to drop onto the broken fan before you drop down to the metal walkway below. Find the big opening in one wall next to the walkway and run down it to return to section c1a3.
Section c1a3 (again): CRAWLWAY EXTRAS AND SILO DOOR CONTROL ROOM
When you come to the end of the shaft, quicksave before trying to drop down to the narrow ledge below. Move along the ledge and enter a vent shaft, then go forward until you come to an opening on your right. Drop down onto a green crate, then turn and crouch-walk under an unbreakable vent grating so you can get to some shotgun ammo. Crouch-jump back onto the green crate under the unbreakable grating, then climb up the grating and crouch-walk back into the shaft.
A short distance past that is another opening on the right, this one with a headcrab not far past it. Approach the opening slowly with the pistol out and the flashlight on so you can sneak-shoot the crab. Go down the crab's shaft until you reach a spot where you can see two marines in the room below you through an unbreakable grating.
You can probably just ignore them and gather the ammo from the room past the end of the shaft without them noticing you, then go back the way you came. If that doesn't work for you, it's best to take out the red-beret marine with a double-barrel shotgun blast through the floor grate that's nearest him before they see you. Shoot the other marine with the assault rifle through that same grate whenever he's in sight, then go for the room with the ammo. (SRC: You probably won't be able to get within shotgun range of them without them noticing you, so stay back in the shaft and use the pistol to shoot them through the floor grate while they're on the other side of the room.)
Go back to the main vent shaft, then turn right and move along until you find a left branch that leads to a room you can drop into. It has a first aid station, two armor batteries, and lots of assault rifle clips. When you're ready to go, jump onto the green crates underneath the unbreakable vent grating, then use the grating to climb back into the shaft.
Go all the way back to the fan room where you first entered this shaft, then move carefully along the narrow ledge to get to where you can drop down to another narrow ledge. Go along it and enter its adjoining vent shaft to get taken back to section c1a3d briefly. Go along the shaft to its end to find a ledge with shotgun ammo that you can drop down to. Climb back into the shaft and return to the fan room, then drop down to the floor and enter the shaft opening that's down there.
At the end of that long shaft, climb up a ladder and get off on the lower of the two small platforms. Use its vent shaft to quickly arrive at the silo door control room. Use the big red button to open the nearby silo door, then pick up the shotgun ammo and leave the control room through its door. Use the nearby first aid and HEV stations if you need to, then go through the silo door and on down to where the "Blast Pit" chapter starts.
Section c1a4: BIG LIFT AND BRIEF RAIL CAR RIDE
Go up to the very left end of the big barricade and look through it to see a bullsquid in the distance. Shoot it down with the pistol, then use the crowbar to bash away all of the barricade material. Shoot the two headcrabs who are among the boxes just past it, then move through the big doorway past them while looking to the right for another headcrab.
Go up the ramp to the small control booth, then move slowly toward the metal door. When you hear the zombie on the other side hitting the door, quickly back off so the zombie won't see you when the door breaks. (SRC: Run up to the lever on the panel, then immediately back up a ways.) Move to a spot where you can toss a grenade through the doorway unseen, then back up before the grenade detonates all of the explosives in that room, killing the zombie.
Check the room to find some grenades and a health pack, then go use the lever on the control booth's panel. That'll bring a big lift up to the lower-floor area nearby, so use the ladder to climb down there. Get on the lift and use its button panel to start it going, then turn around to face the opposite way. As soon as the lift stops, move forward onto the walkway with the health packs, then turn right and drop down to the tracks next to the rail car.
Use your crowbar to whack all the houndeyes that run up to you (or blast them with the shotgun to make sure you don't get zapped), then jump onto the rail car and move up against its control panel. Press the "Use item" key to bring up the speed display, then press the "Move forward" key several times to get the car going at its top speed. (Note that there's one extra speed setting beyond the top indicator shown.)
Crouch down and stay next to the control panel to avoid bullsquid spit as you travel along. Also, keep an eye on your speed display. When it disappears, stand up and look ahead. If you move to the back of the rail car before it stops and throws you, you might could land on the pipe with the open section by leaning on the "Move right (strafe)" key. If so, you could immediately enter the pipe and move on. However, that's a fairly tricky maneuver, and doesn't seem to work in the Source version of the game, so read on for a safer way.
When the car starts crashing through wooden warning markers, quickly back off of it to avoid getting thrown off. As soon as you hit the ground, start running toward the car. It will have stopped by the time you reach it, so jump-crouch back onto it, then get on the two little side beams on its right side and jump-crouch from them onto the ledge.
Turn left and quickly crouch-walk along the narrow part of the ledge to reach a wider part that will allow you to cross the room without touching the toxic water. Before going all the way across, find a spot partway along where you can shoot the bullsquid that's on the other side, but he can't spit at you because a large pipe is in his way.
Go all the way to the end of the ledge and drop down to the dead bullsquid's floor. Crouch-walk under a huge pipe, then climb the ladder that's on its other side. Get up onto the top of the pipe and carefully make your way along to a smaller side pipe that has an open hatch on it. Drop down into that pipe, then move along it until section c1a4k loads.
Section c1a4k: BULLSQUIDS AND TOXIC WASTE
The pipe has another open hatch just ahead. Jump-crouch onto the hatch, then crouch-walk onto the pipe. Jump over to the pipe that's just ahead and on the same level as your pipe. After quicksaving, run along the pipe to where it turns right, then move to where you can jump from the pipe to the nearby railed platform. If you're fast, you'll make it without taking much damage from bullsquid spit.
Pick up some health packs and armor batteries from the table if you need to, then move on to find another large room full of toxic green water. The fastest way to get through this room is to get on the long pipe that crosses the room, then jump from it to the slanty pipe. Get onto the machine next to the lift, then jump onto the lift and crouch-walk over to where you can use its button panel to get it going. Stay crouched until section c1a4b loads to make sure you don't get spit on.
However, you'll be passing up another small table with health packs and armor batteries on it. If you want to go for them, kill both of the bullsquids, then get onto the lift as described above. Face the lift's button panel, then turn right and look along the wall to see the table you're going for. To get there, you'll need to move along the rounded, slanty surface that connects the table's ledge with the machine next to the lift. While moving along that surface, you'll have to be facing away from the green water and leaning on the "Move forward" key as well as the strafing key that'll take you the direction you're wanting to go. On the return trip, you'll have to get off on the long pipe rather than the machine next to the lift. It's probably not worth all the trouble, but it's such a little-known thing, I couldn't resist putting it in.
Section c1a4b: GETTING TO THE ROCKET FIRING AREA
After the lift stops, crouch-walk slowly forward until you can see a bullsquid tail waving around. Get out the pistol and shoot the explosive that's next to the squid until it blows up, killing the beast. Past that, go out onto the start of the long, curving walkway and kill the houndeyes that run up to you. (You could do that with the crowbar, but it's safer to use the shotgun, and you should have plenty of ammo for it.)
Move along the curving walkway until you've got a good shot at the explosives that another houndeye is standing between. Blowing them up will destroy part of the walkway, but you can jump the gap. Before you do, look in the area to the right of it to find more explosives to shoot, killing another houndeye. Check near there for health packs, then shoot the two headcrabs that are on the other side of the walkway gap while standing to where the distant bullsquid can't spit on you.
You could shoot the distant bullsquid with the pistol now, but there'll be a better opportunity for that later. After quicksaving, take a running jump across the walkway gap, then enter the small room with a big red switch between doors. Get out the shotgun, then use the switch to get to section c1a4i.
Section c1a4i: NAVIGATING THE FIRING CHAMBER
As soon as the door to the right of the switch opens, double-barrel the zombie that's just behind it. After you encounter a dying scientist, look for a barnacle tongue hanging down just past him. You could squeeze past it and move on, or you could use it to get to a secret area. The easiest way to do that is to move into the tongue while going past the scientist, then lean on the "Move backward" key right after whacking the barnacle with the crowbar. There's a good chance you'll miss the secret area, so quicksave before you try. If you make it, you'll find first aid and HEV stations that you can use. (Note that you can wait until later to do this one-visit-only secret area if you want.)
To avoid health damage when leaving the secret area, jump over to the wall corner that's past the barnacle and hold down the "Move forward" key. If you don't slowly slide downward, tap the "Move forward" key repeatedly until you drop down onto the walkway. Move on and open the door you come to by using the red switch next to it. Past that is the rocket firing control room. Stand well back as one of the three hideous green tentacle monsters in the rocket firing chamber grabs a scientist and pulls him away. (Despite this, you don't ever need to worry about the tentacles attacking you in the control room -- only in the firing chamber.)
Leave the control room through its other door, then look up to kill a barnacle near a ladder. (You'll need to use your flashlight to help you see it way up on the ceiling.) Climb the ladder and enter the room with the explosive boxes and hand grenades. A stupid, loud security guard will run into the firing chamber and get himself splattified, so stay back and wait for the tentacles to settle down again.
They can't hear you when you crouch-walk, so crouch-walk through the firing chamber doorway and turn left. When you're near the edge of the platform, stop and look down to see a ladder top that's blocked by wooden crates. After quicksaving, toss a grenade so it'll land near the crates and blow most or all of them up. The instant the grenade explodes, crouch-drop off your platform onto the walkway below.
As soon as you land, start crouch-walking in either direction since you may have been heard by the tentacles. If so, they'll start clang-banging at the spot where you landed, and you don't want to be there when they do. If you get hit, quickrestore and try again. Wait until they settle down, then crouch-walk over to the top of the ladder.
Once you make it there undamaged, quicksave again, then look down at the walkway below yours to find a boarded-over doorway. Toss a grenade at that doorway, then hurry down the ladder as soon as the grenade explodes. As before, crouch-walk away in case the tentacles heard you. When it's safe, crouch-walk over to the de-boarded doorway and go through it.
Once you make it, quicksave again in great relief, since it'll be awhile before you have to go back into the firing chamber again. Go along the walkway to reach another room where you need to hit the red switch to switch which door is open. When you use this one, you'll be taken back to section c1a4b.
Section c1a4b (again): CROSSING TO THE OXYGEN AND FUEL AREA
The walkway ahead is blocked by a zombie and a couple of explosive barrels, but that's not the first thing to take care of. Turn right after exiting the door-switch room and move to where you can see the area with a bullsquid. Quickly shoot the explosive crate next to the squid with the pistol, then finish the squid off if the explosion didn't kill it.
Turn and shoot the explosives on the nearby path until they blow up, then slowly crouch-walk across on the blue pipe that survived the explosion. On the other side, break open the two non-explosive crates to find health packs, then move down the corridor past that until section c1a4d loads.
Section c1a4d: TAKING A DETOUR
Move along until you come to an area with an unopenable fuel room door on the left, and a ladder on a metal platform on the right. Don't climb down the ladder, but instead jump over the railing next to the ladder. As soon as you hit the floor, run for the large floor grating ahead. Quickly bash it and start down the long ladder that's beneath it. At the bottom, get off onto the large brown pipe (use the "Jump" key if you have to), then move carefully along the pipe to where it divides.
Go down the left pipe until you reach a short ladder that leads up to a large bashable grating. Before you bash through and climb into the room beyond, use the pistol to shoot down the nearby zombie through the grating. After climbing up, look nearby for a small room with some grenades that you can resupply from. Move down the corridor past that to get section c1a4e to load.
Section c1a4e: GIANT FAN
When you come to a closed door, look on the wall to the right of it for its opening control. There are two zombies just past the door, so toss a grenade at their feet as soon as the door opens. Back up to avoid the explosion, then use shotgun blasts to the head to finish them off if necessary. (Or if you're fast, you can run past them on their right side (your left) without getting hit.)
Past the door is a huge shaft with a giant fan in it. Move around the shaft's upper walkway until you find a ladder you can use to reach its lower walkway. Climb a ladder down from there to reach a short and narrow platform that leads to the fan's button panel. Quicksave, then use the button panel to turn the fan on and immediately start running backwards. Hopefully, you'll be able to make it up the ladder without getting blown around or chopped up by the fan.
Jump into the space over the fan to get blown up to the top of the shaft, where you'll need to use the crowbar to bash through some boards. Once you're floating up above the boards, move over to a large vent covering that's on one wall and bash it out. The easiest way to deal with the headcrab just past the vent covering is to toss a grenade in there, so do that and back away.
After the explosion, move forward to where you can drop into the vent shaft and start moving along it. When you come to a large metal vent covering, turn the flashlight on and carefully shoot a headcrab through the covering before you bash it away. Past that, you'll come to a similar situation with a board barricade. Shoot the headcrab through the barricade, then bash through it to get back to section c1a4d. (SRC: There is no board barricade, so try to sneak-shoot the headcrab.)
Section c1a4d (again): FUEL ROOM
Just around the corner past the board barricade, bash through some metal vent coverings and drop down to find yourself next to the fuel room. There are three zombies and a headcrab in there, though you can't see them all at first. Hang back and use the pistol to headshot the first two zombies you see, then go through the doorway and blast the third one with the shotgun. After that, shoot the headcrab from a distance with the pistol. (It's on top of a green machine next to two red lights.)
Go over to the control panel that's left of the headcrab's machine and use the "OXY ON" and "FUEL ON" buttons. After the lights next to the buttons light up, find the ladder in the alcove to the right of the headcrab's machine and climb it. Use the control on the wall to the right of the door to open it, then head down the corridor on the right to return to section c1a4b.
Section c1a4b (yet again): BACK TO THE FIRING CHAMBER
Return to the blown-up walkway and cross it like you did before (crouch-walking along the blue pipe). In the door-switch room, hit the switch to be returned to section c1a4i.
Section c1a4i (again): BYPASSING THE TENTACLES
Go back to the doorway that leads into the rocket firing chamber, but don't go through it. There's a better way to get down to the next area. Go past the doorway to a red railing, then jump onto the railing and crouch-drop onto the floor below it. You'll lose about 20 health, but it's faster, easier, and more grenade-conservative than making your way down there through the firing chamber. (Note that you can sometimes avoid health loss by getting onto the left end of the railing and hugging the wall on your way down. Hitting the "Jump" key or direction keys as you go may also help.)
As you go along the walkway, you'll come across a wide gap. Quicksave to be safe, then take a running jump across the left side of the gap. Get the shotgun out, then run forward without stopping until you reach an area with a zombie. Quickly double-barrel the zombie in the head to kill it. (Note that this run-and-gun tactic got you across a new walkway breach right before it could happen.) Enter the door-switch room past the zombie and hit the switch to return to section c1a4b.
Section c1a4b (fourth time): CROSSING TO THE POWER AREA
Exit the door-switch room to find that you're in the area with the bullsquid you killed from a distance earlier. There's no need to blow up the walkway, so move past the explosive containers and on to the corridor that's past the dead bullsquid. When the corridor turns right, stop and wait for three houndeyes to run up to you. Blow them all away with the shotgun (or crowbar them if you'd rather), then move forward toward the water spill to reach section c1a4f.
Section c1a4f: RESTORING MAIN POWER
When you come to a large room with hanging cables and barnacle tongues, notice the bullsquid chewing on a dead scientist across the room. The quickest way to kill the squid is to lob a grenade at him, then start firing the assault rifle at him right after the grenade explodes. (However, you could just leave him alone, and he'll never notice you.)
Find the first aid station in the room's opposite corner (to the right of where you enter) and use it to heal up from your rail-hopping incident earlier. After that, get onto the narrow platform that extends out from the main floor, but don't bother pressing the lift-summoning button. Instead, crouch-jump onto the platform's right-hand railing, then jump from there to the ladder you can see against the wall if you shine your flashlight on it (or if you press the lift-summoning button to light the place up).
At the bottom of the ladder, turn to face the short pipe that's right underneath it, then see if you can walk or crouch-strafe off the ladder onto the pipe. If not, you'll have to hit the "Jump" key to let go of the ladder, and you should quicksave first in case you jump too far and land in the toxic water. Once you're on the pipe, jump onto the nearby flooring.
There's a first aid station near where the scientist is standing. A bit farther on is a large pipe that's leaking toxic goo onto the floor. To get past the goo undamaged, take a running jump-crouch onto the pipe, then walk along it until you can drop to the floor past the spill. Quickly double-barrel the zombie in the head, then move past it to find a small movable platform. (If you want to have more fun with the zombie, let it see you, then move back along the pipe so it'll walk through the harmful toxic goo. Keep going back and forth until the goo kills it for you. SRC: The goo won't hurt the zombie.)
Get on the platform and press its button, crouching to avoid the spit of the bullquid that's on the floor far below. After it stops, climb up the ladder it stopped next to, then drop onto the walkway on either side of the ladder. Scrunch up against the wall, since there's a constantly moving platform on your level that'll splattify you if it hits you. (You can actually ride on the thing, but it's not at all useful to do so.)
While keeping a careful eye on the fast platform, move along the wall until you reach the base of another ladder. Right after the fast platform zooms by, quickly move around to where you can climb the ladder. When you reach the top, turn around and walk onto (or jump onto) the large slanty thing nearby. At its top is a red button that you need to press.
Jump onto the top of the reactor where a scientist is "hiding" right after pressing the button, then move across to find another slanty thing with a button at its top. Press the button, then turn and run down to where you can get on a ladder. Climb partway down it, then start watching for the fast platform again. Move to the bottom of the ladder and quickly get against a wall when it's safe to do so.
Make your way carefully along the walkway until you can get back to the top of the ladder that leads down to the movable platform you used earlier. Climb down to the platform (or just carefully drop to it), then use its controls to get yourself back to the area near the toxic spill. Avoid the spill by crossing the pipe as before, then use the first aid station near the scientist if you need to.
Drop back onto the pipe segment next to the big ladder, then climb all the way to the ladder's top. Once there, turn the flashlight on and climb slowly back down the ladder, looking for a small ridge on the large pillar to the right of the ladder. Crouch-strafe carefully onto the ridge and then crouch-walk along it to a point where you can drop onto the floor without taking any damage.
Push and/or pull one of the small metal boxes near the first aid station through the nearby doorway and put it up next to the large metal box. Jump onto the small box, then crouch-jump onto the large box. You can now jump-crouch onto the thick metal cable that runs along the wall. Do so and follow it along until you can drop onto the floor past the now-electrified water spill. Move on past it until you return to section c1a4b.
Section c1a4b (fifth time): RETURNING TO THE FIRING CHAMBER
Move on until you get back to the bridge with the explosives on it. Recross the bridge to reach the door-switch room, then use the switch to return to section c1a4i.
Section c1a4i (yet again): BLAST THOSE TENTACLES!
You have two big walkway gaps to jump on the way back, so quicksave before attempting each one. When you get to the boarded-over doorway, break off the boards with the crowbar, then wait for the tentacles to calm down. You're now going to have to climb all the way back up to the top level of the firing chamber, and that's going to be one heck of a pain. Be sure to quicksave every time you make any progress, and quickrestore every time you take damage.
The first ladder you need to climb is on the left as you enter the firing chamber, so crouch-walk your way carefully over there. Quickly climb it, then crouch-walk away (or toss a grenade) to avoid getting tentacle-pecked. Repeat the process with the next two ladders, and you'll hopefully make it without having to retry too many times.
Resupply on grenades in the room past the firing chamber's upper platform, then return to the control room, watching out for a new floor gap along the way. This is your last chance to visit the barnacle-related secret area (if you haven't already) that's mentioned at the beginning of the first c1a4i section. After you do that, hit the red "TEST FIRE" button in the center of the control panel, then immediately scrunch yourself in a corner next to one of the two doors. Doing so should allow you to avoid taking any damage from the rockets firing. The tentacles, though, will be burned to death. Finally!
Go back to the rocket firing chamber, picking up the pistol that the guard near the explosives room dropped. Use the ladders to climb down to the bottom floor of the firing chamber, then look in the pit in the center to find a ladder. Go around to where you can jump to the ladder, then climb down to its bottom. After quicksaving, crouch-walk your way carefully along the slanty ground, dropping gently down when you have to, until you reach section c1a4g.
Section c1a4g: MOVING ON PAST THE FIRING CHAMBER
After one more minor drop, you'll come to a major drop into a pool of water far below. Do your best to fall into the middle of the water, since landing on the edge of the floor next to the water will mean instant death. Jump out of the water and carefully approach the green toxic spill area to find a .357 Magnum and a box of ammo for it. Look around on the opposite side of the pool for another ammo box.
Move around the edge of the pool to where you can look down in it to see two round holes far below, with the dead tentacle remains being in the left hole. (If you're in the right position, the toxic spill will be to your right.) Dive down and go through the hole on the right, then move forward and up. You'll soon emerge on a platform with a ladder. If you need any health or armor, climb down the ladder and use the first aid and HEV stations down there, then climb back up.
Get onto the large brown pipe that starts just to the left of the ladder platform, then go along it until you can drop onto some pipes a bit lower down. Move along them until you can go no farther, then turn right and drop down to a lower pipe. Run along it until you can jump over to a much larger pipe that has a big gap in it, a small metal panel with a valve wheel on it, and a large open hatch.
First, use the valve wheel to close the pipe gap. (Face the wheel and lean on the "Use item" key until the wheel stops moving.) Then go over to the open hatch and carefully crouch-drop onto the ladder and climb down to avoid health loss. After jumping over the large hole in the pipe segment you just extended with the wheel, crouch-walk through a small fencing hole. Keep going down the pipe until section c1a4j loads.
Section c1a4j: WEAK PIPE AND TRIPMINES
After you turn one last corner in the pipe, you'll come to a large discolored pipe segment that ends in an unbroken fence. When you walk onto the discolored segment, it will break and drop you into the room below. To avoid taking huge health damage, lean on the "Move backward" key as you slide down the pipe. This doesn't always work, so you may have to try it several times. (SRC: That method can help reduce damage, but it doesn't work as well as in the original game.)
If you don't land on the table with the headcrab under it, quickly jump onto that table to crush the crab. That'll also get you some .357 ammo, and some health if you were damaged by the fall. Bash all the crates in the room to find more health packs and five unset tripmines that you can pick up and use yourself. They'll come in handy in the next chapter. Move on down the corridor past the room to reach the point where the "Power Up" chapter starts.
Section c2a1: GARGANTUAN PROBLEM
NOTE: If you're not playing the Source version of the game, you can use two of your new laser tripmines to totally skip this chapter. Run into the gargantua's big chamber, then run through the large opening on the right. If you make it to the concrete barricade fast enough, the gargantua won't follow you in. You can then relax and go about using tripmines to get over the barricade. The way I do it is to set a tripmine a bit lower than halfway down on the middle of the three lower concrete sections, use it to jump onto the top of that section, then move as far right as I can before turning and setting the second tripmine on the upper middle concrete section. (Note that it helps to crouch before setting a tripmine.) Once that's done, the second tripmine can be used to jump onto the top of the upper section, from which you can drop down on the other side of the barricade and move on to the "On a Rail" chapter.
When you enter the large chamber where a gargantua is fighting two marines, run as fast as you can to the doorway that's directly across from where you entered. (It's the only other small doorway in the chamber.) As soon as you're through that doorway, get the shotgun out and look down the hallway to the right. When a vortigaunt appears, shoot an explosive barrel to blow it up and kill the vort.
Pass by the vort's side hallway and continue down the main one. When you reach a broken part of the floor where a pipe is shooting flames, quicksave. Move carefully past the back of the pipe to where a vortigaunt sees you, then back up quickly past the pipe and around the corner. The idea is that the vort will kill itself on the pipe's flames trying to follow you. However, it'll sometimes survive, and you'll get zapped. If that happens, quickrestore and try again. After flaming the first vort, quicksave and repeat the process on the second one.
Crouch-walk up to the floor hole that the pipe is sticking out of, then use the pistol to kill the four headcrabs you can see on the floor below. You may have to move around a little to see them all, so watch out for the pipe's flame. Around the corner past the pipe, go up to the railing and shoot the two headcrabs on the floor below. Carefully crouch-drop down to that floor from the nearest end of the newly broken walkway. (Dang that stompin' gargantua!)
Break open the two crates down there to find a tripmine and your very first pair of assault rifle (AR) grenades. They're very powerful and useful, so save them for a painy day. Skip the ladder for now and go down the hallway to where the four headcrabs you shot from above are. Have the assault rifle out and ready to shoot a vortigaunt a ways ahead, strafing right to dodge its fire if necessary.
As you move toward the downed vort, some rubble will fall ahead of you due to a gargantua stomp. Move toward that spot slowly while looking up with your flashlight on. There's a headcrab near the edge of a ceiling hole, and you can sneak-shoot it with the pistol if you're careful. Or you may find it easier to just toss a hand grenade up there to blow it up before it sees you. Have your pistol ready as you move past that, since two more headcrabs will drop onto the floor ahead of you. After shooting them, move on to where section c2a1b loads.
Section c2a1b: BIG SHAFT AND MARINE CAMP
Past the next doorway is a room full of explosives and vortigaunts. Strafe to where the vorts can see you, then immediately strafe back out of the way so they'll blow themselves up without damaging you. At the other end of their room is a door-opening wheel that you need to lean on in order to open the nearby doors. (If the loud door-opening sound keeps playing even after the doors are open, quicksave and quickrestore to put a stop to it.)
Past those doors, climb up the first ladder and turn left. Move about halfway to the base of the next ladder, then look up. A marine heard you climbing the ladder, and should now be partly visible on the walkway directly above you. If so, get out the .357 and sneak-shoot him. If not, or if he runs out of sight the first time you shoot him, go over to the base of the next ladder to see if you can shoot him from there. If not, you'll have to finish him off later.
Enter the little side room where a bullsquid that you don't have to worry about is dragging a dead marine into a wall hole. Grab both pairs of AR grenades to bring your total up to six. Climb up the ladder to the top walkway, then crouch-walk your way over to the entrance to the marines' area. There's one more marine and a turret to take down (plus the first marine if he got away earlier).
The turret is to the left, so get out your pistol and carefully crouch-strafe to the right while in the room's big doorway until you can see and shoot one of its legs. After it goes down, get out the .357 and sneak to where you can shoot the marine, who's standing in the area around the corner from the first aid station. After the first hit, he'll either move toward you or away from you. If it's toward you, you'll need to shoot him again as fast as you can. If it's away, crouch-walk after him until you can sneak-shoot him again past a couple of corners.
Bash all the boxes and tables in the room to find lots of ammo, including a clip for the crossbow weapon that you won't be getting for two more chapters. What's the point of giving us ammo for it now, I wonder? Anyway, head down the corridor past the room to get to section c2a1a.
Section c2a1a: MARINE HQ AND POWER GENERATOR
When you round the next corner, you'll see some explosive crates ahead. Don't destroy them, since they'll come in handy later. Get out the pistol and edge forward slowly. There are more explosive crates next to a sandbag wall around the corner to the right. There's also a marine at that wall, so shoot the crates to blow them up without letting the marine see you. (SRC: Doing that will make two other marines run into the area, so stay hidden and try to sneak-shoot them. If you can't, let them come to you for up-close shotgun blasts.)
On the way to the sandbag wall, notice that there's a sort of underground bunker-style room with a first aid station and some hand grenades in it. Don't forget about it, since you may need those grenades later on. For now, check past the sandbag wall to find a spare tripmine on the floor near the base of a ramp.
You could take a very big shortcut here if you wanted to. Look over the two sides of this area to see that there are fans below. Jump over the railing and land on the fan that's turning. (SRC: You can't land on the fan, so wait until you're near it, then strafe to keep from being blown back up.) Take the power-restoring steps as described below and ride the lift back up. The place would be full of marines, but you could make a quick run for the exit, using AR grenades to help clear your way, though you won't be safe until you're back in the room where some vortigaunts blew themselves up earlier. I don't advise using this shortcut, but it's cool and different enough that I felt the need to mention it.
Here's the longer, better way. Get out the .357 and quicksave. Slowly back onto the base of the first little ramp while facing the nearest small red-railed balcony. A marine will soon appear on that balcony, and you need to kill him before he can run out of sight. Either hit him in the head with one shot, or shoot him in the body twice very quickly. You should soon hear an explosion, which indicates that the other marine in that area ran into a tripmine and got killed. If both of these things happen, quicksave. Otherwise, quickrestore and try again.
Crouch-walk your way up the ramps to the top, then set a tripmine on the wall to the right of the doorway so that anyone who runs through the doorway will trip the mine and die. While crouching near the tripmine, turn the flashlight on and look through the doorway. Up on the ceiling near some wooden boxes is a vent grating. Shoot it twice with the pistol to break it and let headcrabs start dropping, then immediately run down to the bottom of the top ramp and crouch there, shotgun at the ready. (SRC: Since two marines ran out when you blew up those crates earlier, the headcrab-and-tripmine strategy isn't useful.)
Some marines will probably run out through the doorway and onto the ramps. The first one to do so will be blown up by the tripmine, but you'll have to quickly double-barrel any others that come out. If you stay crouched, they won't be coming out because they saw you, and therefore won't immediately start firing on you, which gives you a big advantage.
After the sounds of battle stop, get the .357 out and carefully sneak your way back up to the doorway. If there are any marines in or near the doorway, shoot them in the head to quickly kill them, then move up against the left edge of the doorway and look down the passage to the right. You should be able to see a computer bank on the left wall past a doorway down there. Shoot it with the pistol until it breaks, then wait for it to start shooting out a continuous stream of fire.
Run down there and jump over the fire stream, then move up against the wall right next to it to see if any marines will notice you and come running. If some do, run down to the bottom of the nearby stairs and watch out for grenades. Marines sometimes manage to get through the flames without dying, so be ready to finish them off with the assault rifle. Also, if a grenade of theirs blows up a vent grating that's over the stairs, shoot the three headcrabs that drop down onto the stairs as soon as they appear.
Go back up to the spot right next to the stream of fire, then quicksave and quickrestore. That might get another marine or two to appear and charge you. Hopefully, that'll be all of them, but you should jump over the flames and search the area to be sure. After that, jump back over the flames and break all the crates down in the area past the stairs to find some ammo, tripmines, and grenades. There are also a few crates to bash in the radio niche near the other side of the flames, plus an HEV recharger and a box with a health pack in it past the big room with the radio equipment and the lift.
ALTERNATIVE: After blowing up the explosive crates when you first enter the area, you could then set a laser tripmine on the wall near the little red-railed balcony that the marine would appear on if you went for the ramps. If you place the tripmine just right, you'll be able to jump onto it, and then from it to the balcony. Quickly shotgun-blast the marine around the corner, then go shoot the "eternal flame" machine and use it to slush all the other marines in the area. This is a trickier way to do things due to the difficulty of placing the tripmine just right, so you're probably better off with the regular way as described above. (SRC: You can't jump onto tripmines that you've set without blowing them up.)
When you're ready to move on, set three tripmines so they'll trip up the marines who'll appear in the area later on. Put the first tripmine on the wall just to the right of the explosive crates near the start of the area that you didn't blow up earlier. Go back up the ramps and through the doorway, then put the second tripmine on the wall just to the right of the doorway. The third tripmine goes on the wall underneath a red light that's a ways to the right of that doorway. (Note that the third one is less useful than the first two, so you may want to skip placing it.) Use the lift's control panel to start it going, then quickly get on it with the assault rifle out. As it descends, look for any houndeyes on the nearby walkway. If you see any, immediately kill them before they can detonate the tripmines that are set around the base of the lift. After the lift stops, move off it to the side and wait for it to go back up.
After making sure that all nearby houndeyes are dead, drop into the water and go over to where you can climb a ladder to get onto the walkway. Do another quick houndeye check, then shoot the explosive barrels you can see down the walkway before you go that way. Wait near where the barrels were for more houndeyes to run up to you, then go down the ramp and find the stairs after finishing off any last houndeyes. Go halfway down the stairs, then turn left and use the pistol to kill the headcrab you see in the distance. Continue to the bottom of the stairs and stop right before you reach the water.
While staying on the last stair that isn't underwater, edge over to where you can see into the watery area well enough to spot the power generator machine off in the distance. Turn the flashlight on to help you see, then use the pistol to shoot the rightmost of the two wooden crates that are next to the generator. When that crate breaks and the generator starts pumping away, go back up the stairs to where you shot the headcrab.
Use the first aid station on the right wall if you need to, then go into the room with the power generator console. Use the button panel that's just to the left of the console to get its green light to come on, then turn around and time your run past the electrical bolt that shoots across your path periodically. You could then use one of the two fans to get back up to the upper floor, but it's hard to do. If you'd rather not, then go back to the top of the stairs and along the walkway that leads to the lift. When you approach it, the lift will start lowering with two marines on it. Let one of them see you, then immediately run out of his sight. He should hit a tripmine and blow himself and the other marine up.
SRC: It's likely that only half of the tripmines will go off, and that one or both of the marines will survive. Be ready to finish them off quickly with the assault rifle. Or after the lift starts lowering, move back to where you can see the nearest low-set tripmine but not the marines. Shooting that tripmine with the pistol as soon as the lift stops lowering should kill both marines.
After the lift finishes ascending, use the button panel that's on the other side of its surrounding walkway to summon it. After it descends again, get on it and ride it up. Have the assault rifle out and ready to go when the lift reaches the top, since there will be a marine near the lift that you'll want to shoot down quickly. If you placed the third tripmine that I advised you to earlier, this marine may run into it. The second tripmine you placed should blow up another marine as he runs to join the fight. (SRC: The explosion will also break open the headcrab vent, so either shoot all the crabs or just run by them and on to where you kill the last marine as detailed below.)
To get the third and final marine, go past the HEV station to the small red-railed balcony. Strafe onto the balcony while facing to the right, then immediately strafe back out of sight. The marine should soon hit the first tripmine you placed and blow himself up. Look around for any supplies you need (and use the HEV station) before leaving the area and going back the way you came. After you pass the underground bunker and move down the hall a short way, you'll return to section c2a1b.
Section c2a1b (again): GOING BACK
Return to the room with the first aid station on the wall, then climb down the two ladders in the shaft past it. Go through the open doors and down the hall to where section c2a1 reloads.
Section c2a1 (again): DEATH TO THE GARGANTUA
As you turn left in the hall, be ready to shoot down a vortigaunt with the assault rifle. Run on until you reach the room with a ladder. Climb up it and use the crowbar to bash all of the boards and boxes that are blocking the door to the track control room. Enter the room, noticing the HEV station on the left wall, and go over to the injured guard.
Grab the .357 Magnum from next to the guard, then move over near the big window to make sure the gargantua comes over to it. Leave the room and jump over the large gap in the walkway. Go carefully past the flaming pipe and on to where you can reenter the large chamber that the gargantua is in. He'll probably see you as soon as you appear in the doorway, and will run over to where he can blast you with his super-heated steam.
The safest way to handle this situation is to blow up the gargantua with grenades. After he sees you and runs over, keep your distance and toss hand grenades so that they land right between his feet. If you run out before the gargantua is destroyed, you can either use AR grenades to finish the job, or go all the way back to the power generator area and get more hand grenades from the little underground bunker room that's near the beginning of the area where you fought a bunch of marines. (Note that you'll have to watch out for a new vortigaunt on the way down there.)
SRC: The gargantua wanders around constantly, making it very hard to lure him over to one particular spot. If you want to kill him with grenades, you'll need to quicksave after every good hit and quickrestore after every miss. It'll take awhile, so be patient and make sure he doesn't get a chance to run up to you and roast you.
A faster way is to lead the gargantua to the big power coil room and fry him there. Before he can sense you and run over to your doorway, run through it, turn left, and run down the large tunnel, hugging the left wall. The gargantua may not follow you into the tunnel if you stick to that wall. If he does, you'll have to run straight for the power coils' activation switch and hope you don't get too badly toasted before the gargantua gets blown up. Note that you don't have to run around to get onto the power switch's higher floor. You can go to the corner on the right past the power coils, then jump up and hit the switch. Stay in that corner until the garger is destroyed to hopefully avoid damage.
SRC: It's easy to make it down the tunnel without being followed if you wait until the gargantua stomps off out of sight down the rail tunnel on the other side of the area. If he doesn't ever do that, try going back down to where section c2a1b loads, then return and keep out of sight. If even that doesn't work, wait until he's on the opposite side of the area with his back turned, then run down the tunnel and hope you can make it to the activation switch before he catches up to you.
If he doesn't follow you down the large tunnel, you can relax. Turn left at the end of the tunnel to enter the coil room, then cross it and go up the steps. Cross the raised walkway to find the switch that will activate the coils. After using it, go back down the steps and through the doorway on the right. At the other end of the small service tunnel, push the door open. Go to the start of the large tunnel and move around until the gargantua starts into the tunnel after you, then quickly run back through the door you just opened. Stand in the doorway at the other end of the service tunnel until you hear the gargantua get himself blown up by the power coils. (If he doesn't, you may have to go up the steps and let him see you on the raised walkway.)
Break open the crates near one of the power coils to find some hand grenades, then return to the gargantua's chamber and get on the rail car. It works just like the one in the first section of the "Blast Pit" chapter. Move the car forward as far as it'll go, then return to the track control room. Use the HEV station if your armor is less than 100, then go over to the big window and use the switch to turn the thing that the rail car is on. (Also, look for some ammo on a control panel a bit to the right of the window.)
Jump through the window to shortcut your way back to the rail car, then get on it and start it moving down the track. After you crash through a barricade, stop the car and use the flashlight to locate a couple of health packs to the right of the track. (SRC: The health packs may not be there.) Ride the car on past that to quickly reach the "On a Rail" chapter.
ON A RAIL
Section c2a2: IMPORTANT MESSAGE AND RAIL CAR ELEVATOR
The rail car will soon stop at a lowered barrier arm. Get off the car and approach the security guard to get him to talk to you. After he's done, use the switch on the wall near him to raise the barrier arm. (SRC: He'll use the switch for you.) Nudge up against him to get him to walk out onto the track in front of the rail car, then get on the car and use it to run over him. He's of no further use, and that's as fun a way as any to dispose of him. (SRC: Get him to follow you, then lead him over to where he'll shoot the barnacles that are over the rail car elevator.)
Quicksave before moving onto the rail car elevator, since there are four barnacles on the ceiling above it. You can probably ride the elevator down and then move on without getting caught by a tongue. Quickrestore and try again if you do get caught, maybe changing your position on the rail car. If you keep getting caught, move to where you can look up and shoot all the barnacles before riding the elevator. At the bottom, ride forward through the electrified water until section c2a2a loads up.
Section c2a2a: ARMOR BATTERY AND HOUNDEYE PLATFORM
As you move forward, you'll pass under a place in the ceiling that has a headcrab in it. It'll probably just jump from one ceiling part to another, so you can ignore it. After you go up a ramp and leave the zappy water, you could actually abandon your rail car and go through the rest of the chapter without using rail cars at all. That isn't the best way to do things, though I will use that fact to provide shortcuts every now and then.
Soon after the car turns right, you'll reach a place where an armor battery is setting on a small wooden platform on the right. If you need armor, you can stop right next to it and get it. (SRC: The battery will be beneath the wooden platform. To get it, get onto the platform and bash it with the crowbar. After falling into the water, swim back to where you can use a ladder to climb onto the houndeyes' side area mentioned below.)
Move on around the corner past the battery, then stop the car and put it in reverse. Back all the way up to where you're next to a side area that has three houndeyes bouncing around in it. Quickly kill them all with the assault rifle, then park the rail car next to their floor in a spot where it isn't blocking the red ladder that you can see going down into the water. That's so you can use the ladder to exit the water after dropping down into it.
You may want to skip that, but if you drop into the water and use the flashlight to help you see, you'll eventually reach the entrance to an underwater tunnel (crouch as you approach it) that leads to a spot where you can get some bullets from next to a dead security guard. To avoid drowning and to help avoid all the zappy little leeches, drop into the water from a spot past the front of the rail car, then move along with your head above the water's surface as much as you can. When you have to be underwater, go as fast as you can, and only stop to crowbar-whack a leech if it's going to run into you. (SRC: There aren't any leeches.) After you get the bullets, head back the way you came and climb the ladder to get onto the houndeyes' floor.
Enter the nearby corridor and move along it to get to where section c2a2b2 loads. It's also totally optional, but it includes many good things, including your first C4 satchel bomb.
Section c2a2b2: OPTIONAL SIDE AREA WITH C4 SATCHEL BOMB
Just ahead is a big side room to the left. There's a bullsquid in it over to the right as you look in the doorway. You could easily sneak-shoot it with the pistol, but there's a funner way to deal with it. Get out the assault rifle, then move into the room far enough that the bullsquid will see you. Immediately run back out of the room and down to the end of the hallway to find a room with three houndeyes in it.
Use the assault rifle to spray the houndeyes to interrupt their whiny charge-ups. After all three of them are dead, return to the hallway you came down to find that the bullsquid you got the attention of in the side room is now fighting a bullsquid that magically appeared in the hallway when you entered the houndeyes' room. After one of the squids is killed, quickly shoot the other one until it dies, too. (SRC: Sneak-shoot the bullsquid in the side room, then go up the stairs and sneak-shoot one or two of the houndeyes before finishing them off with the shotgun.) Look into the watery area that's next to the houndeyes' room to find yet another bullsquid to kill. Shoot the explosive barrels down there if it's next to any of them, then finish it off.
All of that probably took quite a few bullets, so go back to the big side room and search near all the bodies for ammo clips. If you need shotgun ammo, approach the big red "BLAST DANGER" doors at the back of the room to open them, then crouch down and move forward until you can see the feet of a marine who's standing on the other side of the rocket. Don't shoot him, but wait for him to be attacked by headcrabs. Finish off the survivor(s) with the pistol, then run back there and grab his shotgun. Avoid the headcrabs that drop down nearby by immediately running back through the blast doors. Whether you do all of that or not, return to where you shot a bullsquid in the water.
Use the switch that's on the wall near the watery room to extend a bridge over it, then drop down into the water if you don't have five tripmines. There's one in the water near the green crate. After you get it, jump-crouch onto the crate, then do a running jump-crouch over to the nearest wall ledge. If you crouch fast enough after jumping, you won't get zapped by the dangling electrical cable. Turn left and hop onto a higher piece of concrete, then move onto the bridge.
Kill the two barnacles in the room past the bridge with the crowbar, then use the .357 to sneak-shoot the bullsquid that's in the room past the nearby railing and crates. Use the flashlight to help you see the squid between the leftmost crate and the wall, or bash that crate with the crowbar to get a better view (though be sure to strafe to avoid the squid's yecchy spit).
To get to the squid's room, use the short hallway that connects your room to it. (Crowbar the barnacle in that hallway just like you did the other two.) Be sure to jump-crouch onto the large green crate to get the C4 satchel bomb that's on it, then smash the wooden crates to find bullets and hand grenades. When you're done, go back the way you came (watch for headcrabs in the hallway) until you return to section c2a2a.
Section c2a2a (again): FINDING A WAY OUT OF THE TRACK LOOP
Get back on the rail car, then ride forward until you go up an incline. Stop the car just past the incline and jump onto the narrow ledge that leads along the left side of the track that branches to the left. You can't take the car down there, but you can walk over and bash a couple of crates to find .357 ammo in one of them.
Just past that is a track branch to the right. You can't go down it in the car yet, so stop the car just past it, then get onto the narrow ledge to the right of the car. Use it to crouch-walk your way down the right-side track branch until you reach the ledge's end. Sneak to where you can see a headcrab in the area just ahead, then shoot it with the pistol to make sure it won't be a nuisance when you go by it in the rail car later on.
Go back the way you came and get on the rail car, then ride it around the next corner. Crouch to avoid getting zapped by a dangling electrical wire, then move forward slowly to where you can see two houndeyes in an area to the left. Stop the car long enough to shoot them with the pistol, then move the car forward slowly until its front end is just past the track switch device. Edge over in the car until you can see part of a bullsquid around the corner past the switch.
Sneak-shoot the bullsquid with the pistol until it leaps into the air. When it does that, a nearby elevated turret will see it and activate. Shoot the squid to get it to jump again, and the turret will start firing at it. It can only hit the squid when it's in the air, so keep shooting it to make it jump until the turret kills it for you. That'll save a bit on bullets.
Now you need to ungratefully take down the turret so it won't give you any trouble when you get to its area later. Slowly ride the rail car forward, looking up to the elevated walkway where the turret is, until you can see part of it. As with other turrets, shoot it in the leg with the pistol until it goes down in smoke.
Ride the rail car around another corner, and stop it just past the four-way track intersection. Get out on the right-hand ledge and follow it along like you did before. It's rather short, so move to its very end, then look for a bullsquid in a side area ahead and to the right. You should be in the perfect position to sneak-shoot it, so use the .357 to do so.
Get back on the rail car and ride on until you get near the next track switch. Shoot it with the pistol before you reach it so that it'll flip, causing your car to go straight on the track instead of turning right and going by the houndeye area that you're already done with. After you pass the switch and turn left, decrease your speed to the minimum until after some large rubble falls ahead of you. Speed up again, but watch for a platform on the right that has a bullsquid on it. You'll want to stop the car in a spot so that the squid is mostly behind a pillar, and you can shoot it with the pistol without it being able to spit back.
Move the car up to where you can jump over the platform's side rail, then find the ramp that leads down to a lower floor. If you dive down into the water, you can find a .357 Magnum next to a dead marine, plus an armor battery. To avoid the leeches in the water, use the usual tactic of moving around on the surface, only diving to see where something is or to pick it up. (SRC: As before, there aren't any leeches. Also, the Magnum is just for show, and you can't get any ammo from it.) To get out of the water, climb up the ladder that's in one corner.
After quicksaving, carefully jump over the rail track where it starts to slant upward. Move along the floor past that to reach a spot with two crates that you can break open to find an armor battery and hand grenades. Go back to where you can jump onto the rail car, then ride it forward very slowly. One of the local barnacles has its tongue hanging directly over the track, and you'll want to kill it with the pistol before passing under it.
Ride on until you come to the side area where you shot down a bullsquid before. Park the car next to the floor, then watch near the stairs for a headcrab to come toward you. Kill it with the pistol, then get off the car and look around for a first aid station plus items near both dead marines (including under the stairs). Go up the stairs and bash some crates to find a .357 Magnum and to clear the passage to the room with the turret you shot down earlier.
Also in that room is a switch you can use to move the crane that's blocking the exit route near the first track switch. (You can see it out the room's window.) Return to the rail car and ride on until you reach that track switch, not forgetting to duck the live wire along the way. Shoot the switch to flip it, then ride along the track past the moved crane until section c2a2b1 loads.
Section c2a2b1: MARINES VS. VORTIGAUNTS
Move the car slowly forward until you can see a marine's legs up on a higher walkway ahead. Shoot those legs with two .357 bullets to kill the marine, then carefully move the car forward to where you can get off its right side and onto the lift. Don't move the car far enough forward to activate the lift, since that'll cause you to have to fight two marines that you can skip.
Climb the ladder that leads up to the marine you just shot, and turn right as soon as you reach the ladder top. You don't want the marines in the nearby lift seeing you. Use the first aid station if you need to, then grab the bullets and AR grenades from near it before climbing up the next ladder. Past the ladder top, push the wooden crate to the left a bit so you can crouch-walk past it on its right side.
There's a marine on a board across the tracks a bit to the right, and you're going to want to carefully sneak-shoot him with the .357. After you do, break open the wooden crate to find a box of .357 ammo. Crouch-walk down the ledge to the right of the tracks until you pass the dead marine and get to where you can see a sandbag wall in an area ahead. There'll be a marine back there who sees you and runs around (and possibly throws hand grenades your way), so shoot him down with the .357 as soon as possible. (If he doesn't appear at first, try jumping across the track and moving around.)
Move back along your ledge until you can see down the side track. If you see any vortigaunts near the lowered barrier arm down there, shoot them with the pistol to see if you can get them to run around to where the marines will shoot them (or vice versa). Move forward along your ledge until you get around to a spot where you can see some marines in a kind of "between the tracks" area to the left. Keep crouch-walking back and forth between that spot and the one where you sniped at a vortigaunt until doing so doesn't cause any more fighting between the marines and the vorts.
Crouch-walk all the way to the big gun that's set up behind one of the sandbag walls and use it to finish off any marines or vortigaunts that you can see ahead. (SRC: The marines may turn around and see you before you can reach the big gun, so you may prefer to sneak-shoot them with the pistol or .357.) Jump over the track to reach the marines' area, then crouch-walk forward slowly to see if there are any vorts left in the area across the next track. If so, quickly shoot them down with the assault rifle or .357 Magnum.
Break open the boxes in the marines' area for supplies, then jump across the track to where the vorts were. Go up the stairs and shoot two headcrabs plus any vorts who are hiding up there, then crouch-walk along the walkway that leads to the HEV station. You need to be careful to not let the marines you skipped earlier see you. (They're on a lift a ways below the walkway.)
Return to the bottom of the stairs and jump back across the tracks to the big gun emplacement. Find the stairs past the big gun, then hop onto the side railing and slowly move up it. When you're to where you can clearly see the head of the marine who's standing in the area past the stairs, get out the .357 and deliver a carefully aimed head shot to kill him instantly. Jump up to get the attention of another nearby marine, then quickly drop down to the bottom of the stairs and wait for him to appear at the top so you can .357 him, too.
Past the top of the stairs, raid the radio area for health and ammo, then go to the start of the nearby corridor. (Stay out of the left-side room, since it just has a marine hiding in it.) You'll see some vorts ahead fighting some marines, so hang back and wait for that to be over. When it is, move to where you can shoot some vorts to lure them back to you one at a time for easy killing. When you've gotten all you can, move into the corridor to get section c2a2c to load.
Section c2a2c: ANOTHER BIG MARINE-VS.-VORT BATTLE
Quicky finish off any remaining vorts, then go into the large side room and break the two boxes that are on the floor to find .357 ammo. Go along the walkway past the side room until you come to some stairs. Crouch down at the top of the stairs and crouch-walk carefully to where you can sneak-shoot the marine at the bottom of the stairs with the .357. Or toss your C4 satchel down there to blow him up. You'll be getting more soon. (SRC: He may not be there due to the fact that the nearby conflict between marines and vorts has probably already triggered. Do watch for other marines near the bottom of the stairs, though.)
Crouch-walk into the dark space under the bottom half of the stairs and break the crate there to reveal an armor battery and a floor grating. Bash the grating and drop down through the hole, then move along until you come to a place with a dead marine. As you approach the marine, use the flashlight to look past him. Quickly shoot the headcrab that appears, then look around to find some supplies, including two more C4 satchel bombs.
While you were gathering those supplies, some marines and vorts were having a fight in the area above you. Climb up out of the secret area and crouch-walk slowly down the corridor to the right of the stairs to see who survived the fight. Quickly shoot them down, then go around and collect ammo from the dead marines. Also, jump across the tracks to find a large alcove with two crates you can smash for more supplies. (SRC: If there are any surviving marines above the secret supply area, they may see you and shoot you through the gratings. You may prefer to go kill them off before going for the supplies.)
If your armor is less than 100, go all the way back to the HEV station in the previous section to charge up, then come back here to continue. Crouch-walk carefully along the ledge that's on the left side of the track that leads away from this area until section c2a2d loads.
Section c2a2d: MORE MARINES-VS.-VORTS AND A BUNKERED MACHINE GUN
Crouch-walk forward until you reach a kind of stick-out pillar, beyond which is a raised ledge with a red railing. There are three marines on that ledge that you need to carefully sneak-shoot with the .357. Quicksave before you start, and crouch-walk forward very carefully to get to where you can see part of the next marine in the series, but he can't see you. You should be familiar with this routine by now.
After they're all down, move forward to where you can climb some stairs to reach their ledge so you can collect their ammo. To get off the ledge, hop up on the railing next to the stairs, then run forward. You should drop onto the ground safely past the electrified rail. (It's harder to jump it from the bottom of the stairs, though you can walk across it without taking damage if you stay on the black-and-yellow-striped things.)
Move up to the big doorway that leads to the next area, but retreat and hide in the corner to the left of the doorway as soon as you hear vortigaunts teleporting in. Have your shotgun out in case any vorts or marines run into your sight, but stay in your corner until the sounds of fighting stop. Go carefully through the doorway and finish off the survivors with the assault rifle. (Note that one vort likes to hide in a dark niche on the left side of the area.)
Get the crowbar out and bash the boards off of the doorway on the left, then go inside and get out your shotgun. Move around next to the security guard until a vort teleports in just outside the doorway, then quickly blow it away with a double-barrel blast to make sure the guard survives. Bash the boxes in the room to get some .357 ammo and health, then get the guard to follow you into the room across the hallway.
Run toward the wooden boxes in that room to get the ceiling to partially collapse and drop headcrabs (or stay back and shoot the ceiling with the pistol), then quickly retreat while your guard kills the crabs for you. After they're dead, go over to a spot next to the first aid station that's behind the wooden boxes, then turn around and toss a hand grenade up into the ceiling area to kill off the last two crabs. You can then get up there by jump-crouching onto the single box, then jump-crouching onto the two-box stack, then jumping onto the ceiling ledge. Check the back of the ceiling area for three armor batteries, then drop back down to the floor. Break the boxes to find another armor battery, then use the first aid station if you need to.
Whack the guard for his pistol, then quicksave before moving down to the other end of the area. There's a marine manning a heavily sandbag-protected big gun there. One way to handle this is to run over and stand behind the big wooden crate on the right until the gun stops firing. Bash the crate with the crowbar, then immediately run forward and jump the track. It's possible to do this without getting shot, though it's likely you will be. You can then move up next to the sandbag pile and jump up and down in order to see and shoot the marine who's in there manning the gun.
The other way to take him out is safer, but requires the use of a grenade. Get behind the big wooden crate on the left, then crouch-strafe slowly to the right until you can see the very right edge of the gun itself. Toss a hand grenade or AR grenade so that it'll go through the gap to the right of the gun and blow up the marine. You should quicksave right before tossing the grenade so you won't have to use more than one.
After the gun's rendered inoperable, jump over to its side of the track if you're not already there, then jump onto the slanty cement beam that goes up to a horizontal crossbeam. Jump-crouch onto the crossbeam, then jump across to a narrow ledge that you can use to jump onto a beam with an armor battery on it. Slide carefully down the slanty beam on either side, then move along the ledge next to the track until you can press up against the big red "BLAST DANGER" doors.
After they open, back up to a safe distance and use the pistol to detonate one of the tripmines that are set just past the doors (or carefully crouch-walk under them without detonating them). Past the doorway, crouch-walk slowly toward the top of the ladder, looking down on the walkway below for a marine. If you're careful, you can sneak-shoot him with the .357 before he sees you. Climb down the ladder and go through the doors near the marine to find yourself another rail car.
Before you get on it, search the room to the right to find a health pack and some .357 ammo in a wooden crate, then check out the area just past the room to find a hidden HEV station in an easy-to-miss wall niche. Get on the rail car and ride it forward slowly while crouched and pushed up against the control console. When you're in between the two red laser alarm beams, stop the car and stand up just long enough to see where a bullsquid is situated a ways ahead of you.
Use shoot-and-duck tactics to kill that bullsquid with the .357, then slowly move to the right on the car so you can sneak-shoot the bullsquid over on the walkway to the left. After it's down, crouch-ride the rail car until it's next to some steps on the right. Get off the car, but don't go up the steps. To avoid brushing against the turret and activating it, jump onto the railing that's to the left of the steps and crouch-walk your way along it until you're well past the turret.
After getting the AR grenades from near the dead bullsquid, use the rail-walking trick to get back past the turret and onto the rail car. Ride it forward until you come to a ledge on the left with a turret and a door. Stop the car and open the door, ready to shoot the bullsquid past it with a .357 slug and strafe left to avoid its toxic spit. After it's dead, move slowly into its room and use the pistol to sneak-shoot a headcrab that's hiding around a corner on the right. (There's a chance that another headcrab is just past the door on the left, though the bullsquid usually kills it.) Go to the back right corner of the room and crowbar-whack the barnacle there, then look around for supplies before returning to the rail car. Ride onward to where section c2a2e loads.
Section c2a2e: ROCKET EMPLACEMENT AND SIDE AREAS WITH BARRIER-RAISING SWITCHES
As you round the corner, be crouched down and moving slowly. As soon as you're past the corner, strafe left off of the rail car without stopping it. Wait and watch as it continues onward, killing the rocket emplacement operator by detonating a tripmine that he stupidly set too close to his position. As soon as he's dead, move along the ledge you're on to reach his area and find a health pack and his dropped gun. (SRC: The tripmine probably won't kill the marine, so crouch-walk along the ledge until he starts firing rockets at you. They'll all go over your head, so ignore them and shoot the marine's leg until he dies.)
Keep following the ledge along until you approach the area where the rail car was stopped by a lowered barrier arm. Get out the .357 and slowly crouch-walk along the left ledge until you can see and shoot a vortigaunt that's in the area on the other side of the tracks. Sneak carefully along, edging around another annoying stick-out pillar, until you can shoot the next two vorts across the tracks. (You could sneak-shoot the vorts, but that would take more ammo than letting them see you and immediately shooting them right in their big red eye for an instant kill.)
There's another nearby vort that's a ways to the right of the last two you shot, but it's not your next target. Slowly crouch-strafe left, watching the hallway that leads off from the main vort area, until you see one coming down the hall after you. Kill it, then crouch-strafe left some more until the second vort that's down the hall comes after you. You're then probably almost "left" enough to see and shoot the final vort in a corner to the right.
Jump across the track and find a first aid station to the left, then go down the hall to find some green crates blocking access to some stairs. Stand back and shoot one of the tripmines past the crates with the pistol, then jump-crouch onto the single crate and walk across it. There are two headcrabs in a ceiling area just past the crates, but you probably don't have to worry about them. Toss a hand grenade up there if you want to be sure, though. (Quicksave first in case the grenade bounces back at you.)
Crouch-walk up the stairs to make sure you're not seen, then bash the two crates to get a C4 satchel bomb. Get out the .357 and crouch-walk carefully over to the corner past those crates. You can probably sneak-shoot both of the marines in the area ahead, but each one will charge you as soon as the first slug hits him, so you'll have to finish him off quickly. After they're down, check their room to find an HEV station and a large switch on a panel that'll raise the nearby barrier arm.
Hop onto the nearby railing, then carefully crouch-drop to the floor below. Jump over two tracks, then go left to find a new rail car to use. (If you go back for your old one, a marine will have taken control of this one by the time you get back here.) Ride this car down the track until you encounter another lowered barrier arm. This might be a good time to abandon the rail car and proceed on foot. That's doable, and not too hard, but I'll go ahead and tell you how to keep the car.
Get off the car by moving onto the left ledge, then move back along it until you can see three wooden crates stacked on the upper walkway in the big side area. Use the pistol to shoot the bottom two crates to pieces (automatically destroying the top crate), then use the .357 to blast the three marines that start running around up there. To avoid wasting ammo, only shoot at them when they're briefly standing still in one of their favorite standing-still spots. (SRC: The marines will be able to shoot back at you and throw grenades, so take them down as quickly as you can. Note that some may hide to where you can't shoot them without entering their area.)
Now to take care of the fortified heavy gun that's on the right side of the area. Jump across the track right before the point where it splits, then move forward and around the corner. Quickly crouch as you run toward the base of the upper floor that the gun emplacement is on. Quicksave if you made it uninjured, then get out your hand grenades. Move back a short distance so that the gun will be firing but not hitting you, then toss a grenade so that it goes over the gun's sandbag wall and lands behind it, killing the marine at the gun when it explodes. You'll know if it worked because the gun will stop firing.
Hop across the tracks to get to where you can climb up a short ladder to reach the upper walkway. Look along it for a first aid station and some dropped guns, then go over to the gun emplacement and use the wall switch that's right next to it. Return to the rail car and ride on until you come to the next rail car elevator. Stop the car short of the elevator, and check out the side area. There are some C4 satchel bombs in crates, plus one underneath the small personnel elevator. (Send the elevator up, then drop down to get the satchel and climb out using the ladder. You can then recall the elevator.)
Get into the elevator and ride it up to find yourself next to a large stack of explosive crates. Get out your C4 satchels and toss one through the gap between crates. (Move up to the gap and jump right before tossing the satchel.) Ride the elevator back down, detonate the satchel, then ride the elevator back up. Pick up the satchel that's near the elevator, then look for a splattified marine's dropped weapon next to two crates that you can bash for supplies.
Slowly crouch-walk your way along the rim of the rail car elevator shaft to reach a small red-lit room with two AR grenades in it. Look down and across the shaft to see some marine legs to shoot. (Use the pistol to save on .357 ammo.) Crouch-walk back across the shaft rim, then find the long ladder near the elevator. Climb down to the bottom to claim the dropped weapon of the marine you just leg-shot, then climb all the way to the top of the ladder to find some boxes you can bash for ammo.
Climb down the ladder to the floor with the elevator, then carefully strafe off the ladder to land on the floor. Take the elevator down, then get on the rail car and ride it up the rail car elevator. Crouch down as you ride forward past the elevator's top to avoid getting zapped by electrical discharges from the nearby machines. As soon as you're past those machines, strafe left off of the rail car without stopping it. It'll go on ahead, detonating some tripmines, and will stop a ways past that. As you walk along the left ledge to catch up to it, section c2a2f will load.
Section c2a2f: ANOTHER TRACK LOOP
When you catch up to the rail car, hop onto it, but don't start it up yet. Look ahead to see two large wooden crates to the right of yet another barrier arm. There are marines hiding behind those crates, and they'll bust the crates and open fire if you move toward them. Stay where you are and get out the assault rifle. Shoot the crates to pieces, then shoot the marines, who will be too far away to return fire. (SRC: The marines will be able to return fire, so shoot out the left crate and then quickly kill them with the .357.)
After they're both down, crouch-ride the rail car forward until it stops, then crouch-walk off of its right side and go grab the marines' guns and AR grenades. Use the switch on the wall to raise the barrier arm, then quicksave. It can be a bit tricky to crouch-jump your way back onto the rail car. When you make it, get the car started again and ride on to a spot where the track curves left.
At this point, you could stop the car and get off of it. You could go right and then left (using the side ledges to walk on, as usual) to shortcut your way to the long ladder that leads down to the next section. However, I'll assume that you'd rather take the long way, which can get you some more bullets. Crouch-ride your way through another area with crates going across it, and keep crouch-riding until you're past a rocket emplacement.
As soon as you are, stop the car and walk over to the emplacement. The marine will just stand there and let you crowbar-whack him and take his gun. What a dope! Past the next corner, stay crouched to avoid zap damage until you reach a track switch. Shoot it with the pistol to flip it, then back up a little if necessary (still crouching) so the car will go straight past it instead of turning left. Keep riding along until the car stops at the edge of a rail car elevator shaft. Get off of the car and start climbing down the nearby ladder to reach section c2a2g.
Section c2a2g: ANOTHER BUNKERED GUN AND AN OUTDOOR SNIPER
As soon as this section loads, stop moving and drop a hand grenade. (SRC: Go a ways back up the ladder right after dropping the grenade so you won't take any damage.) It'll blow up some tripmines in the area below for you, plus knock over a turret without getting the others all riled up. Go down the ladder until you can look up to see the doorway to a small supply room, but don't go so far down that you'll hit the red laser alert. While still on the ladder, toss two hand grenades so that they'll land inside the supply room and blow up the zombies in there.
Jump off the ladder to avoid hitting the laser alert, then go into the supply room to find lots of hand grenades and a first aid station. Leave the supply room and make your way carefully past the turrets on the left side of the track. When you come to where the track turns left, quicksave. Run and jump over the track, then quickly run up behind the nearest large wooden crate.
Crouch down and push the crate a little to the left so you can see and shoot the marine at the small sandbag wall ahead. Use the .357 for a good instant-kill head shot. He probably won't fire at you, but if he does (or if both of the nearby crates get destroyed), quickrestore and try again. If both crates survive, bash the nearest one and push the other one ahead of you as you move toward the marine's sandbag wall.
When you reach it, bash the crate to get a tripmine, then go around the wall on its right side. You'll then be able to run up next to the mounted gun's sandbag wall and shoot the marine who's in there by jumping up and down so you can see him. Go down the corridor past their area, and start crouch-walking when you come to a doorway that leads outside. There are two marines out there facing the other way and gossiping about you. Get out your C4 satchels, jump-toss one their way, back up, and detonate it. Instant splattification for both guys! (SRC: Go through the doorway and up to the railing before jump-tossing the satchel.)
After claiming their dropped weapons, turn left from the bottom of the steps and go all the way forward, jumping the rail track on the way. Look up to see a bit of camouflage netting up on the cliffside. That's the first sniper of the game, and you'll want to take him out. The easiest way to do that is to throw a grenade of some sort up there, so do so. (I recommend using an AR grenade since you'll be getting more soon.) You'll know when you get him because he'll make a few gasping and choking noises.
Look for a streetlamp with a crate and a health pack on a machine next to it. Jump onto the machine from on the crate if you need health, then bash the crate to get shotgun ammo. Find the large "BLAST DANGER" doors near the streetlamp and open them by using the controls on the wall to the left of them. Go through them and use the next set of controls to move on to section c2a2h.
Section c2a2h: LAUNCHING THE SATELLITE
There are three marines in the area that's ahead and to the right, and the big mounted gun that's to the left isn't the best way to deal with them. Crouch-walk your way very slowly along the right wall until you can sneak-shoot the leftmost marine with the pistol. The other two are harder to sneak-shoot, but it can be done. Or you could quickly duck out of cover long enough to launch an AR grenade at one of the marines to take him out quickly, then back up and shoot the last one when he runs into view.
If you're not playing the Source version of the game, you can use a shortcut here. Jump-crouch onto the smaller sandbag wall, then jump-crouch across to the small ledge that's to the right of the "BLAST DANGER" doors. (Note that it's a hard jump to make, and you'll usually just slide back down to the ground.) Once you make it, turn left and get onto the slightly higher ledge, then jump-crouch onto the window. You can't enter the launch control room, but you can go over to the left side of the window and hit the launch button through it (even if you can't see it). The following hints will assume you don't use this shortcut.
Go through the big "BLAST DANGER" doors that the marines were guarding and down a short hallway to reach a room with stairs that are "guarded" by laser alerts connected to big explosive packs. Push the shorter of the two large metal crates all the way to the back of the side area it's in, then jump-crouch onto it. Move to a spot near its left edge (left as you're facing the stairs) and jump-crouch onto the stairs' side rail. You can then move forward, turn right, and go through the door at the top of the stairs.
SRC: Pull the smaller crate out of its side area, then pull the larger crate out far enough for you to get behind it and push it to the back of the side area. Push the smaller crate up against the larger crate, then jump-crouch onto the smaller crate. You can then jump-crouch onto the larger crate, then jump onto the stairs.
Past the door, turn left and crouch-walk slowly along the left wall to where you can sneak-shoot the two marines with the .357 Magnum. They may run around after the first hit, but you should be able to finish them off without being seen. Check the first room for a first aid station, then go into the second room and use the big red button that's between its two windows to launch the lambda satellite rocket.
After the rocket's away, the door in your room will reopen, and you can go back the way you came. When you come to the explosive stair trap, carefully crouch-drop off the top of the left side of the stairs. Go back to the big red doors that you entered this section through, and use the control panel on the wall nearest the closed doors to get back to section c2a2g.
Section c2a2g (again): SUPPLY ROOM AND UGLY OLD RAIL CAR
Turn left at the tracks to find a newly revealed area with a side ladder. Climb down it to reach a room with supplies and a new rail track. Break open all the wooden crates and check the tops of the two biggest green crates, then get on the ugly old rail car. Do not start the thing up, since it'll just make things harder in the next chapter. Instead, jump-crouch onto its front end and crouch-walk forward and to the right so that you'll drop down onto the ledge to the right of the track. You can then follow that ledge along to reach the "Apprehension" chapter.
Section c2a3: MILITARY AMBUSH AND SILO
Keep going along the right-hand ledge until you approach the open area that's on the right. Three marines are stationed there, but they haven't been alerted to your presence, so you can fairly easily sneak-shoot them all with the pistol. Or you can let them see you, then run way back along the ledge to where you can see them in the distance, but they won't be able to fire at you. Shoot them with the pistol whenever they appear (use the flashlight to help see them) until they're all down. (SRC: They can fire at you long-range, and usually won't run into view if you're really far away, so use the sneak-shooting method.)
Grab their weapons, then go through the door in their area and start down the ladder. When you near the point where it's broken off, strafe right so you'll fall into the water without hitting the crate. Bash the crate to get some shotgun shells, then push open the underwater door and go through it. Go down the corridor and through another door, then quickly run up the stairs on the left to get to where you can breathe again.
Check the floor past the stairs for an assault rifle clip, then go through the doorway and along the unbroken walkway. No need to dive and bash the padlock off of the underwater barrel cage! In the next room, use the assault rifle to kill the zombie under the stairs plus the one halfway up them, then check the under-the-stairs area for some bullet clips. At the top of the stairs, use the first aid station if needed, and bash the crate for an armor battery.
Past the next doorway, go along the walkway to the right and bash the crate to find another bullet clip, then go back to where you can crouch-drop onto the large black-and-yellow-striped divider wall. Turn and move back to where you can drop onto a crate, which you can then bash for an assault rifle clip. Jump over the railing and dive down, then quickly go for the underwater doorway that's to the right. Swim through the underwater passages as fast as you can, ignoring rather than bashing the little leeches, until you reach section c2a3a.
Section c2a3a: ICHTHYOSAUR TANK AND CROSSBOW
Keep swimming along, passing by a door on the right, until you come to a spot where some rubble partially blocks the passage. You'll have to sort of "crouch-swim" through the rubble, and then do the same thing with the next bit of rubble. Past that is a hallway that you can surface in to catch your breath and get your "drown damage" reversed.
Dive down and look for a nearby floor grating. Bash it with the crowbar, then swim down through it. Take a right at the path intersection, then look for a spot where you can swim up and bash another grating. In the room beyond it, you can surface for air again, then dive and look around on the floor for lots of AR grenades and crossbow ammo. When you're ready to leave, find the door with the big computer bank in front of it. Push up against the side of the computer bank to knock it over, allowing you to leave through the door.
Past the door, go straight and then turn right to finally leave these underwater passages behind. You'll soon come to a room where an ichthyosaur playfully eats a scientist. You can kill the ichthyosaur safely by standing next to the pool and shooting it with the assault rifle and/or shotgun whenever it's visible on the surface, but that takes a lot of time and ammo, and isn't recommended. (However, it would make getting the crossbow a bit safer.)
Make your way carefully around to the other side of the room, watching out for slick wet spots and barnacle tongues. At the other end of the walkway is a side area with a ladder that leads up to a big room with a talkative scientist, plus first aid and HEV stations. Go on past the stations and along a metal beam to reach a spot where you can drop down into a hanging cage and grab a crossbow weapon (right after quicksaving, of course).
Move around in the cage until it falls into the water, then swim up through the gap at the top and turn left. Swim toward the underwater doorway you see in the wall as fast as you can. Hopefully, the ichthyosaur won't be able to bite you at all. If it does get you once, keep going, since you can heal up at the wall stations in the scientist's room. If you get chomped multiple times, you should quickrestore and try again. (You could kill the ichthyosaur with the crossbow before exiting the cage, but it could be tough to do that and then surface before drowning.)
Or instead of dropping into the cage, you could drop down onto the top edge of it so that you're almost directly above the crossbow. If you crouch-walk very slowly forward, you should be able to pick up the crossbow as you fall past it and into the water. The underwater doorway you need to swim for will be just ahead and to the left, so you should make it easily without becoming fish food.
Once you're back on the walkway, go carefully along it to get back to where you're next to the entrance to the side area with the ladder. Go into the side area if you need to use its wall stations, then return to the walkway. Look to the back of the ichthyosaur tank to see a door next to a broken-off walkway. Get the crowbar out and run-hop along the water to where you'll get caught by the barnacle whose tongue is hanging down right next to the end of the broken-off walkway.
When it catches you, look up so you can whack it when you get close enough. As soon as you do, lean on the "Move forward" key so you'll land on the walkway. Go through the door, then through the doorway on the left. Go down some steps until you reach an underwater area with a couple of crossbow clips. Get them, then go back the way you came and on down the corridor until section c2a3b loads.
SRC: The barnacle tongue method won't work, so you'll have to use the underwater gate. Drop into the water and quickly go into the corner that's to the left of the broken-off walkway. Dive down and find the gate and its red wheel nearby. Surface for air, then dive back down and use the wheel (lean on the "Use item" key) until the gate is most of the way up. Quickly go under it and along the passage until you can surface for air, then go back and make sure you picked up all the crossbow ammo that's near the gate.
Section c2a3b: TWO-ICHTHYOSAUR TANK AND GENERATOR PISTON ROOM
Go up some steps and through a door to find a room full of barnacles. Stay near the door and kill them all with the shotgun, then shoot the top of the large crate that has shotgun shells setting on it. That'll cause two vortigaunts to teleport in, so quickly retreat past the door for cover. After you shoot down the vort that appears on the walkway, sneak over to where you can see the other vort down on the floor below and shoot it down, too.
It's now safe to go down to the floor and bash crates to find lots of shotgun ammo. Move down the short hallway to the next room, which has a broken-up walkway and two ichthyosaurs swimming around in the water. Go to the end of the first big walkway segment, then turn left so you can see a hole in the fencing in the back corner of the room. After quicksaving, run-hop along the surface of the water and jump through that fence hole. It can be kind of hard getting through the hole, so quickrestore if you mess up and the monster fish get you. (You might try jump-crouching through the hole to see if that helps a bit.)
As soon as you're past the fence hole, dive down and swim quickly along the underwater passage until you reach a ladder. Climb up it to a large room, then run down the side passage you see just ahead and to the left. At its end is another ladder, so climb it to get onto the upper floor. The reason for the rush is that a bullsquid saw you climb out of the water, and probably followed you at least part of the way down the side passage. If you can't see it from the upper floor, climb back down the ladder and crouch-walk slowly around corners until you can sneak-shoot it. (Use the crossbow, since you have plenty of ammo for it.)
Get back up on the upper floor if you left it, then crossbow-kill the second bullsquid that teleports in on the lower floor. After that, go down the passage at the other end of the upper floor to find a side room with lots of good ammo. Also, follow the walkway past the side room to find yet another clip for the crossbow. It's going to be your main weapon until you lose everything near the end of the chapter.
Return to the upper floor of the big room. You could use the switch on the control panel to get the huge pistons going and jump across the room on them, but that's not the best way, even though it gives you access to a small side platform with C4 satchel bombs on it. Instead, push the small metal box so that it falls down onto the floor below, then drop down after it. Push it up against the large green crate in the back left corner of the room, then jump onto the metal box and jump-crouch onto the green crate. (SRC: Use the upper floor's large metal box instead of the small one.)
Bash the wooden crate to get it out of the way, then go forward and up the ladder to get onto the walkway above. Go along that walkway until you reach a short hallway with a first aid station at the other end. Run down that hallway and turn the corner quickly, then edge back to where you can crossbow the bullsquid that teleported in behind you without it being able to spit on you. Or just skip that if you don't need to use the first aid station. (SRC: You probably won't be able to sneak-shoot the squid without it coming after you.) Go on past that until section c2a3c loads.
Section c2a3c: FREEZING ROOM
After you turn the next corner, you'll come to some steps that lead up into a room with two rows of computer banks. There are several vortigaunts and headcrabs hiding among the computer banks, so get out the crossbow and slowly crouch-walk into the room, looking to the right for your first targets. After killing a headcrab and two vorts, go forward to the back of the room and look for the last vort around the corner past the first computer bank. After it's down, look behind the second computer bank for the final headcrab.
After you kill them all, the scientist in the glass-walled side room will open the door for you. After using the HEV station and getting the shotgun shells from a table, go through the door and hear what the scientist has to say (or not). Use the hard-to-see button to the right of the big B-shaped door, then go through it and look to the right. Quickly kill the vort at the other end of the freezer room with the crossbow, then get out the assault rifle and look for two headcrabs hiding behind the large pillars nearby.
After you get both of them, use the crossbow to kill the vort in the short hall that connects the two freezer rooms. (If you're careful not to get hit by crabs or vorts, you'll only be losing armor at a very slow rate, and won't have to worry about it.) In the second freezer room, shoot the two headcrabs with the assault rifle without letting the vort see you, then move to where you can sneak-shoot it with the crossbow.
After it's down, go back to the big B-shaped door in the first room and use the button panel to the left of it to reopen it. Go to the nearby HEV station and recharge your armor, then reenter the freezer area and run over to where that last vort was standing. Quickly crouch down and move onto the ladder, then climb down it and jump off. Go down the next ladder to reach the floor, then go forward a bit to reach section c2a3d.
SRC: Your armor will be taking damage from the cold much faster than in the original game, so you might want to just get out your assault rifle and run through the freezer area, dodging headcrabs and AR-grenading the vorts. Better yet, kill off the vort in the first freezer room with the crossbow from near the doorway, then go charge your armor back up before doing the AR grenade run-through.
Section c2a3d: ASSASSIN ROOM AND DIRTY AMBUSH
Bash two large wooden crates to find health packs, then turn the corner with the crossbow out. Go into zoom mode and shoot down the two vorts that are in the hallway ahead. To get over the odd floor snag near the start of the hallway, go over it on its right side. There are two more vorts that'll teleport in when you move far enough down the center of the hallway, but there is a way to avoid them appearing.
To bypass the vorts, you need to get on top of the first wooden crate that's along the right side of the hallway. Jump-crouch onto the barrel that's nearest that crate, then jump-crouch from it to the crate. Jump the gap to get to the top of the next crate, then drop down onto the floor past it. You can then turn around and bash three crates for supplies, but the vorts will appear if you try to pick up the AR grenades. Turn and head to the big lift at the end of the hallway.
Use the lift's button panel to elevate yourself to where a security guard gets killed in the middle of an important message. You could actually save his life by whacking him once with the crowbar before he gets shot, but there's no use in that, since he won't follow you around or shoot at assassins, and you'll have to finish the crowbar-whacking job if you want to get his gun. (SRC: A crowbar hit will kill him, and he won't drop a gun.)
Bash the wooden crates near him for supplies, then get out your tripmines and quicksave. Place a tripmine just to the left of the doorway that's in the concrete wall straight ahead. Crouch just before placing it to make sure it gets set down low. Quickly back up a ways and move up against the right wall, then wait for the assassin who saw you to hit the tripmine and die. If she manages to glitch her way through it without triggering it, quickrestore and try again.
The other two assassins can probably be sneak-shot with the crossbow if you're quiet enough. Crouch-walk up to the spot where you placed the tripmine, then turn right and crouch-walk slowly toward the larger doorway you see on your right. The second assassin is a little past it. Shoot her in the leg with the crossbow as soon as you can, then go past her and a brown door. Move toward the next corner carefully, since the final assassin is just past it, and you'll want to sneak-shoot her with the crossbow, too. (SRC: The final assassin will always come out and attack you when you sneak-shoot the second one, so spam her with AR grenades.)
If you're at less than 100 in health or armor, find the recharging stations in the room past the doorway you set the tripmine next to. Don't bother bashing crates or hunting for ammo, since you won't need to use any more until after you get ambushed and robbed. (Note that bashing crates will get you an armor battery if you need it.) Go up the ramp that leads to the raised floor area, then look for the large lever marked "Surface Access."
Go over to the lever and lean on the "Use item" key until it's moved all the way to the left. Go back down the ramp and through one of the newly opened doors that has a "SURFACE ACCESS" sign next to it. Enter the room with the first aid station in the back of it to get yourself conked, robbed of all your weapons, and dragged off to section c2a3e.
Section c2a3e: TRASH COMPACTOR
As soon as you regain control, do a quicksave, then run forward and start jumping up onto boxes. There's really no need to rush, so after you run forward to reach the lowest boxes, take your time to carefully crouch-jump up the boxes without falling off and losing progress. You should easily make it up onto one of the room's side ledges without getting squished. (SRC: The trash compactor moves much faster, so you'll have to really rush to make it to the ledge.)
Wait until the trash compactor stops moving, then quicksave and quickrestore to make sure the compactor's two halves are being displayed properly. Use them to cross the room so you can grab the crowbar from the ledge on the other side. Climb down the nearest ladder and use the flashlight to help you find a grating on the floor. Bash the grating out, then drop down into a large pipe. Move along it to get to the "Residue Processing" chapter.
Section c2a4: ENTERING THE PROCESSING FACILITY
After you fall out of the pipe and into some water, turn right and get out of the water. Go through a short tunnel to reach a big outdoor area in which two headcrabs will teleport in and drop down nearby. It's best to avoid them, so enter their area running, and swerve left into the water as soon as you can. Run-hop across the water, then run over to the silo-like structure with a ladder on it.
Go to the right of the silo to find a valve wheel that you can use. You don't need to hold down the "Use item" key on it, so as soon as you start it turning, run up the ladder. The wooden platform inside the silo will already be lowering, so quickly drop onto it before it gets down to where dropping onto it would hurt you. (If you take some damage, but not much, play on -- a first aid station is coming up soon.) Ride the wooden platform until it stops, then crouch-walk into the rusty pipe opening. Move along in the pipe until section c2a4a loads.
Section c2a4a: TOXIC WASTE VATS
At the other end of the pipe, bash out the grating and watch as a security guard kills a couple of headcrabs for you. You could rush ahead to kill the barnacles that the guard will soon stupidly get himself caught by, but there's no use in doing so. Just drop down to the floor and follow him along, grabbing his pistol after he gets eaten. (Along the way, be sure to get the bullet clip that's on the floor near the start of the curving hallway.)
Use the crowbar to bash the three barnacles that the guard leads you to, then use the first aid station on the wall past them if you need it. Go down the hallway to the left of the first aid station to come to another bashable barnacle near the top of some winding stairs. Move down to the bottom of the stairs to find an HEV station, but watch out for the two headcrabs in the small area to the right of the stairs' bottom.
You really shouldn't need any armor at this point, so it's best to just go back the way you came without wasting any time or bullets on the headcrabs. Return to the room where you dropped down from the pipe and find the ladder on the side of the big hazardous waste vat. Climb it and jump to the big chunk of gunk that's directly ahead of you, then take a running jump at the pipe entrance past it, crouching right before you land on it.
Follow the pipe along until you reach a ledge in a large room full of waste vats that have big up-and-down mashers over them. You need to cross the room using the two mashers directly ahead of you. Jump to the nearest masher as it's just coming up out of the green sludge, then wait if necessary to jump across to the second masher. Just be sure to jump before the first masher reenters its green sludge. Right after you jump to the second masher, jump onto the big pipe past it. (Don't worry if you take a bit of toxic damage, as you'll be able to heal it soon.)
Walk along on the big pipe as far as you can, then turn right and jump to the other nearby big pipe. You should end up in a spot past its weak section, so follow it along to the big waste mixing vat, crouching when necessary. Before you cross the vat, drop to the room's lower floor and run around to where you can use a first aid station. You can also go through a door to reach the area with two headcrabs and an HEV station. Crowbar-whack the headcrabs, then use the HEV station (and the first aid station again) until you're back to 100 health and 100 armor.
Climb up the ladder that gets you back up next to the mixing vat, then jump to the center part of the nearest mixer. For the jump to the second mixer's center part, wait until the mixing arms are lined up between the two centers, then quickly jump across using them. (SRC: The mixers are moving very fast, so try to jump from the end of the first mixer to the second mixer's center, crouching right before you land. If that's too hard, very carefully crouch-walk along one side of the tank until you reach the exit pipe, then crouch-drop into it.) After that, you can just run forward to land on the open pipe's edge. Crouch-walk your way into it, then move along until you reach section c2a4b.
Section c2a4b: UNDERWATER DETOURS AND MASHER CONVEYORS
When you reach the room with conveyor belts, bash all the wooden crates for health and ammo before you start riding on the big slanty conveyor. After you drop down into some water, turn around and enter the large underwater pipe with the big "DANGER" sign over it. Surface in the next room and get up onto one of the side ledges, then go down a short hallway and drop into the water again.
Dive down and go through one of the two small underwater openings, then surface in the next area and move along until you turn a corner and see four flame vents in pipes above you. Crouch-walk past them to avoid damage (standing up very briefly if you get stuck while crouch-walking), and continue crouch-walking along until you're past the big underwater roller gadget. Swim quickly for the area on the right where you can surface and breathe again.
Get up onto the floor to find yourself in a room with a first aid station. The door past the stairs in that room just leads back to previous areas, so get back in the water and swim on. You'll soon surface in a room that has three conveyor belts with small mashers over them. Turn left and jump up onto the ledge, then get out the pistol and look through the nearby window. Shoot the bullsquid you can see through the window until it's dead, jumping right before each shot if you need to. (Note that crouching briefly after each jump-shot can help you avoid the squid's spit.)
Cross to the ledge on the opposite side of the water to get a .357 Magnum, then enter the bullsquid's room and find a first aid station, two C4 satchel bombs, and two armor batteries. Be sure to grab both satchels, as you'll need them in the areas ahead. Leave the room and go along the ledge to find the conveyor control panel in the room at the other end. Quickly run into the room, hit the middle switch on the control panel, and run back out before the nearby bullsquid can spit on you.
Go over to the window in the dead bullsquid's room that has a button panel next to it. Carefully watch the two mashers that are above the rightmost conveyor belt to get a feel for their timing. You need to hit the button when they're both up, then quickly run to where you can jump onto that conveyor and crouch-walk under the mashers. Quicksave before you try, since this can be a rather tricky thing to do. As soon as you're past the mashers, uncrouch and run along the conveyors until section c2a4c loads.
Section c2a4c: RIDING THE CONVEYOR BELT MAZE
When you come to the end of the current conveyor belt, carefully drop down onto the next one. Just ahead are two hazard areas where you have to avoid various mashing machines. The first set are horizontal piston-style mashers, and the second set are vertical stomp-style mashers. Each individual masher has its own timing, and you'll need to hang back and study each one so you'll know when the ideal time to run by it is. (And need I say to quicksave before you start, and after passing each set of mashers?)
After you crouch-walk past a spot beyond the last masher, look for a conveyor belt below the one you're on to drop down to. As soon as you're on it, turn and go against its direction of movement. Keep going until you reach a spot where you can move across to a parallel conveyor belt. Do so, then hang back on it while looking ahead. There's a laser tripmine a ways ahead that you'll want to carefully shoot out with the pistol before you get very close to it.
After it's gone, walk along the conveyor until you're stopped by a cross-conveyor. You can easily crouch-walk under it, but don't do that yet. Instead, get out your C4 satchels and toss one onto your conveyor after quicksaving. Wait until it reaches the corner ahead, then detonate it. That should blow up the tripmine that's around the corner, so crouch-walk under the cross-conveyor and go see. If the tripmine is still there, quickrestore and try again.
Once you eliminate it, go into the big room with the large rollers. When you get near the first roller, jump over to the conveyor on the left. When you get near its next roller, jump back onto the right conveyor. Quickly crouch down as you approach the tunnel that the conveyor is going into, then crouch-walk forward until you reach the next room. Quickly strafe right off of the conveyor and get into the nearest corner. There are some big mash-jaws in the middle of the floor, and headcrabs will be dropping into them.
Wait until the jaws are opening, then run forward to where you're next to them. When they close again, crouch-walk onto them and allow yourself to drop down when they open. If you drop carefully enough, you won't lose any health from the fall (but it's okay if you do). On the conveyor belt below the jaws, you could try to jump off the end of it to the ladder you see ahead, but it would be easier to turn and move off the side of the belt onto the metal walkway. Walk over to the ladder and climb it, then go down the red-lit corridor until you reach the "Questionable Ethics" chapter.
Section c2a4d: CAGED ALIEN GRUNT AND BLUE LASER ROOM
At the end of the red-lit corridor, climb the ladder as far as you can, then bash the grate. Don't climb up any more yet, though. Turn around on the ladder to where you can see a houndeye, then throw your last C4 satchel toward him while looking upwards. The satchel should land on the floor near the houndeye. Climb back down the ladder and move forward a bit, then detonate it.
Get the crowbar ready, then climb up the ladder and into the room above, ready to quickly whack any surviving houndeyes (though there shouldn't be any). Grab the box of .357 ammo from the middle of the floor, then go through the open gate to find a first aid station near an open door.
SRC: After bashing the grate, turn so that you can see the nearest houndeye, then wait if necessary for it to turn its back to you. While facing it, edge slowly up the ladder until you can toss your C4 satchel into the houndeye group. (If it gets stuck on the edge of the ladder's hole, it won't work.) Climb back down and detonate the satchel to kill all of the houndeyes, then climb up and enter their room. Jump-crouch onto the metal crate that's next to the fence, then avoid touching the fence while edging over to where you can crowbar-bash the red electrical thing with the wire attached to it. Soon after you do, the gate will open.
After healing up, go through the door and on until you reach a room. Go around on the right side of the alien grunt cage that's in the middle of the room and crowbar-bash the glass that's covering a button. Immediately run around the back of the cage to where you can see the door that's to the left of the button. As soon as it opens, run through it and down the hallway until you reach the next room. Hopefully, the alien grunt won't be able to hit you with any hornets.
In the large blue-ish room with the headcrab cage in the center, enter the small control booth to find a first aid station and a big button. Hit the button to temporarily close all of the room's doors and zap the headcrabs with a powerful laser blast. Doing this will cause a marine to magically appear just outside the room's exit doorway. You'll want to get his attention and quickly run back into the control booth and hit the button. The best way to do that is to back out of the control booth until he sees you, then run forward to the button.
Stay away from the control booth's door while the laser is building up charge, since the marine may be setting grenades next to it. When the zap sequence is over, look around for his dropped assault rifle. Past the laser room, you'll find another first aid station, and then a security guard around the next corner. Wait until he's done talking to you, then get him to follow you and move ahead to where section c2a4e loads.
Section c2a4e: LOBBY COMBAT, BLUE LASER ROOM #2, AND TRIPMINED COMPUTER ROOM
After you round a couple of corners, you'll be looking into a large lobby with two marines standing directly ahead of you, facing the other way. After quicksaving, launch an AR grenade at them. You want to kill both marines with that one grenade, and they make it difficult by starting to run the instant you launch it, so you may have to quickrestore and try again several times. (You may eventually decide to settle for killing just one of them with the grenade.)
Move into the lobby while looking to the right. If there are any marines on the upper walkway near the railing, start shooting them with the .357. Hang back so they'll have to come down the lobby's side hallway after you, and you should be able to take them down with a minimum of damage to yourself. Get the assault rifle out, then cross the lobby and go down the side hallway and along the walkway near the railing to make sure you got them all.
NOTES: After the marines start attacking you, you can run back down the hallway to where the previous section loads, then turn around and return to this one. That'll "freeze" the marines where they are, and make them forget about you, which allows for some sneak-shooting. Also, you'll probably want to keep your security guard alive by leaving him behind. You won't need his help if you use the "freeze 'em" trick.
After collecting all of the marines' dropped weapons (including the shotgun), return to the lobby and get the shotgun shells off the desk, and use the HEV charger on one wall. Return to the previous section briefly to use a first aid station (and to get the security guard to follow you if you left him behind), then go back to the lobby hallway and move along until you reach the next big blue overhead-laser room.
Leave your security guard follower outside the room to keep him from getting killed. Enter the room and push the button that's on the wall between the two cages to open them, then run for the control booth. Headcrabs can only be killed by the zappy laser if they come out of their cages, so you may have to go over there and lure some out, being careful not to let them hit you. As soon as one or more come out, run for the control booth and hit the button to kill them.
Repeat that until all of the headcrabs are dead, then search both of their cages to find a crossbow and some snarks. Past that room is a corridor with two marines in it. They probably won't be alert to your presence yet. If they are, you'll want to shoot them down fast or try to lure them into the laser room for zapping. If they're unaware of you, it would be easiest to carefully move to where you can sneak-shoot them with the .357.
At one end of their hallway are some doors you can open to return to the lobby's side hallway. At the other end is an entrance to a room full of computer banks, one of which is rigged with multiple tripmines. In that room, go left from the little shelf with two armor batteries on it to find a dead marine with three unset tripmines near him. Pick them up, then set one of them right near that spot.
Go up the sloping floor to the red-lit room, then go over to its large window. Get out the pistol and shoot one of the tripmines, then immediately crouch down and stay crouched until the sounds of battle stop. Stand up so any survivors down there will see you, then quickly run to the start of the sloping hallway and get your assault rifle out. Hopefully, there'll only be one survivor, and he'll get killed by the tripmine you set.
SRC: When you get to the computer bank room, you may find that the tripmines have already exploded, and the alien grunts and soldiers are already in the room (though they haven't started fighting yet). There seems to be a glitch that explodes those tripmines whenever you load a save that you made anywhere in this game section. Didn't the stupid idiots who made the Source version ever play-test anything? Jeez! Anyway, approach the room's doorway slowly so you can sneak-shoot the nearby alien grunt with the pistol. After it's down, crouch-walk slowly into the doorway to get the other grunt and the three marines to fight. When the sounds of battle stop, quicksave, then try to sneak-shoot all of the surviving marines (preferably with the pistol to save on .357 ammo).
Make sure every enemy is dead, then grab one or both of the armor batteries on the shelf if you need them, plus the marines' weapons. Go back the way you came and get your security guard to rejoin you, then return to the computer room. Past it, you'll soon come to the start of a winding hallway. (SRC: You may find it impossible to get the security guard down to that hallway. Another *#^@ pointless glitch! Oh, well. Might as well whack him for his pistol.) Sneak-shoot the marine who's at the left end of the hallway with the .357, then move down the hallway until you come to a door on the left.
You could greatly shortcut the process of leaving this building by moving up against the door, facing the left side of it, and hitting the "Use item" key. That should activate the panel that opens the door, even though it's on the other side. (SRC: This won't work.) Go through the door, shut off the crazy "surgical unit" by using the control panel to the left of the walkway, get a scientist from the back room to follow you, then retrace your steps all the way back to the lobby. (Note that you may have to keep talking to the scientist to get him to continue following.) Once you make it, skip ahead to the last paragraph before section c2a4g. This shortcut is very highly not recommended because you'll skip getting the gauss gun, so read on from here for the longer and better way to do things. (Though note that you'll want to open the door and shut off the surgical unit now to make things easier later.)
Go down the hall to the room with several crates in it. Break all of the crates with the crowbar except for the one that a tripmine is aimed at. Move around it on either side to get bullet clips, plus access to a first aid station. Return to the hallway path split and go the other way to find an area with several glass-fronted headcrab cages. Run around in front of the cages until the crabs break the glass, then move to a safe location and use your pistol to help your guard pal shoot them.
After you make sure you've gotten all of them, including the ones that don't jump out of their cages right away, go past the cages to find a set of doors that you can go through to return to the lobby. Check its side hallway to see if a marine has appeared in it, and shoot him down from a distance with the pistol if he has. Use the lobby's HEV station if you need armor, then return to the headcrab cage area and go up the stairs that are between cages to reach section c2a4f.
Section c2a4f: USING THE PRIMARY LASER
Move up to a spot near the top of the second set of stairs, then wait and listen for the sounds of marines fighting bullsquids to stop. Get out the crossbow and peek around the corner in zoom mode. If you see a squid twitching around near a large crate in the distance, switch to the pistol long enough to shoot out the crate and let the squid get to the marine it's after.
There's usually at least one marine survivor in the distance. If so, shoot all the ones you can see in the head with the crossbow, then move forward until you reach an open doorway on your right. There may still be a bullsquid in the room past that doorway, so move to where you can sneak-shoot it with the pistol. Continue on down the main hall, watching the area at the other end carefully for marines.
SRC: Since marines can see you and fire at you from greater distances, use that fact to your advantage. Peek around the corner at the top of the stairs to get a marine to see you, then go back down a few steps and get out the shotgun. The marine(s) should see the bullsquid in the side room as they come after you, and start fighting it. You can either take advantage of the distraction to charge them, or you can wait on the stairs for any survivors to come within range of a double-barrel blast.
When you get near the end of the main hall, check the room on the right to make sure it's marine-free, then break all the boxes outside the room to find some ammo. That plus the marines' dropped weapons should end the ammo crisis for now. In the marines' room, pick up a couple of odd-looking ammo boxes from the shelves and use the first aid station if you need to, then press the big red button on a panel to start a laser up.
Down a short side corridor near the marines' room is a similar room with houndeyes in it. Quickly kill them with the assault rifle or shotgun, then press that room's big red button to get its laser going. Go back down the main hallway until you find another branch to the right with some explosive crates in it. Move into that side hall just far enough to start hearing voices in the distance, then stop and wait until the guard who's handling an experimental weapon overcharges it.
Go down the side hall and into the room beyond. Pick up the experimental gauss gun (also known as the tau cannon) from the floor, then find and use this room's big laser-starting button. Return to the main hallway and go back to the room where I had you sneak-shoot a bullsquid earlier. Get the armor batteries that are on the shelves if you need them, then hit that room's laser-starting button.
Go back down the main hall to the primary laser room. You should see the big laser device being fed two beams of energy. Push the movable crate over to where it'll get in the way of the laser shield when it lowers, then press the big yellow button on the nearby console to fire the laser and make a big hole in the wall.
After the laser stops firing, go over to the hole and crouch-walk slowly through it so that you can drop down to a small metal ridge that's against the wall a bit below the bottom of the hole. Walk along that ridge to the nearby corner, where you can drop onto a square joint on a vertical pipe. From there, drop down to the next small metal ridge that's against the wall, and then to a curved section of pipe below it to get section c2a4e to load up again.
Section c2a4e (again): LEAVING THE BUILDING
Drop down to the floor, then go up some steps and through a door to reach a small room where three scientists are hiding out. Your next task (if you haven't already done it by using a shortcut) is to cross the adjacent room and turn that evil, whirling "surgical unit" off. Who in the world would use a monstrosity like that for surgery? Dr. Frankenstein wouldn't touch that thing! Anyhow, after quicksaving just in case, run and jump across the left side of the room when it looks safe.
After you make it, use the sparking control panel to shut the freaky machine off. If part of it blocks the walkway in the center of the room, turn it on and then back off again until the walkway is clear. Use the blinky-light panel to the right of the doors to open them, then go talk to any one of the scientists to get him to follow you. Exit the surgery room, then turn left and lead the scientist through the hallway with the broken-open headcrab cages. (He may stop following you when you approach this hallway, so talk to him to get him going again.)
Go past the cages and on until you get back to the lobby. Check the lobby's side hallway to see if there's a marine there, and assault him with the assault rifle if so. Walk up to the retinal scanner that's to the right of the lobby's big exit doors and wait for the scientist to unlock the doors for you. Use the nearby HEV station if needed, then go through the doors and the big turnstile-like thing past them to reach section c2a4g.
Section c2a4g: TWO HIGH-UP TURRETS
When the outer doors open, quickly crouch-walk through them, and stay next to them as they close (but don't let them close on you). There's a marine nearby that you'll want to sneak-shoot with the .357. After he's down, go over to where the dead scientists are, then turn around and look up at the top of the nearby wall.
Get out the pistol and slowly move back to where you can see the very top of a turret. Shoot it down, then move back to where you can see the other turret and shoot it down. If you're careful, they won't be able to shoot you at all. Turn and shoot the explosive crates blocking the path ahead, then go past them to find some crates you can break open for armor batteries and .357 ammo. Go up to the big door past that to get the huge, fun "Surface Tension" chapter to start.
Section c2a5: CHOPPER AND ICHTHYOSAUR AT THE DAM
Use the button panel to the right of the door to open it, then run through before it closes again. Don't run far, though, since there are marines hiding around both corners ahead. Use the pistol to sneak-shoot both of them, then get out the assault rifle and go down the central path until you can see a couple more marines ahead. Quickly fire an AR grenade at them, then back up and shoot them as they appear ahead of you. (Note that it might be safer to shoot out all the explosive barrels in the area first.) You could instead try to sneak-shoot the first one with the crossbow, but that's very hard to do. You could also toss your five snarks their way before they see you, then retreat and wait for them to run into view for quick shooting.
After they're down, check around for health packs and go back through the big button-opened door to where you found armor batteries if your armor is less than 100. Return to where those last two marines were to find yourself near a small dam. At the other end of the dam is a sandbag-protected mounted gun that you'll want to take out right away.
When you first approach the dam and hear the Apache helicopter start up, quickly shoot at the sandbag-protected gun with the assault rifle. You should eventually be able to blow it up. If you're fast enough, you won't even have to duck for cover from the chopper, though don't hesitate to do so if necessary. (SRC: The assault rifle will bounce up and down a lot as you fire, so many of your bullets will miss. You might want to use the pistol instead, or a fully powered altfire blast from the gauss gun.) As soon as the gun emplacement is blown up, turn left and run for cover in the nearby dark corner. While you're there, the chopper won't be able to see you or shoot you at all.
Stay there and let the game run for awhile. The chopper will be flying back and forth, shooting at the ichthyosaur that's in the water on one side of the dam. You're going to have to enter that water, so it would be in your best interests to wait until the chopper kills the monster fish for you. You can't really tell when it does, so you'll have to periodically quicksave and run for the water, then quickrestore and wait some more if the 'saur is still alive. (If you get impatient, you could finish it off with the shotgun and/or assault rifle. Stay in the corner where you drop into the water to avoid getting chomped, and shoot the big fish when it's above water.)
Before you drop into the water, you could destroy the chopper with two fully powered altfire blasts from the gauss gun and still have enough ammo to do so again in the next section, but I found it easier to avoid getting shot up by just dodging the chopper rather than shooting it down. (SRC: One fully powered altfire blast will destroy the chopper, so you might as well do that to begin with, and then kill the ichthyosaur.) In any case, dive into the water next to the dam, then swim over to the small tower structure and climb up the ladder on its side.
Inside the tower's small room, use the first aid station if needed, then use the big button panel to turn its button red. After quicksaving, dive into the water and locate the valve wheel that's on the dam wall, fairly far down. It's easy to spot since there's a red light near it. After you find it, you'll probably want to surface for air, then dive back down and go straight to it.
You'll need to go up to it and lean on the "Use item" key until the wheel stops turning, then quickly turn to the right or left and move into the fan area past the grating you just opened. Crouching will probably help you get past the grating and the fan just beyond it. After you push past the fan, you'll find yourself in a small tunnel that leads to the other side of the dam. Stay in the tunnel and above the water's surface until all of your drown damage is reversed, then swim forward to leave the tunnel. (SRC: You'll be unable to stay in the tunnel.)
There's a large boulder ahead with an armor battery on it that you might want to go for after making sure the chopper isn't right overhead. After that, swim along under the surface of the water until you reach a closed underwater gate. Climb up the ladder that's on the wall to the right of the gate, then enter a large tunnel and make your way along until section c2a5w loads.
Section c2a5w: FOUR-PART OUTDOOR AREA (RIGHT HALF)
When you exit the tunnel, you'll be in one section of a big four-part outdoor area. You could turn left just past the tunnel exit to find three headcrabs and a cave with a health pack in it, but that's not really worth the trouble. Instead, go forward from the pipe exit to find boxes to bash for ammo and a ladder on the left wall to climb.
From on the ledge at the top of that ladder, you could turn and jump across to a small supply area, but you're probably better off waiting to collect those supplies until later. Run quickly along the ledge to find the next ladder, which will get you up to higher ground. Hide in the area just past the top of the ladder and get out the gauss gun. After quicksaving, come out of hiding long enough to hit the chopper with two (SRC: one) fully powered altfire gauss blasts. If you do it right, it'll go down in flames.
Kill the houndeye that's running around if the chopper didn't do it for you, then go through the gap between the two huge rocks that are just to the left of the electrified fence. You'll soon emerge into an empty-looking outdoor area, but there are several marines hiding in various spots. If they've somehow been alerted to your presence, you'll have to back up and take them down as they run after you.
Otherwise, use the following attack plan. Get out the shotgun, then run along the left side of the area, passing a sign and two large boulders. Just past the second boulder, turn left and double-barrel the marine who's hiding there, then quickly run into the nearby dark tunnel. Stay on the right side of the tunnel and stop when you reach a corner. From it, you can turn and shoot marines who appear at the tunnel entrance without them usually being able to shoot back.
A safer way to assault the area is sneakily with the crossbow. Turn right after entering the area and crouch-walk your way along the rocky wall, looking toward the two huge rocks that are over to the left. When you get to where you can see the legs and right arm of a marine who's standing between those rocks, get out the crossbow and quicksave, then go into zoom mode and shoot him.
If he runs off after the first hit, look to the left for him to appear. If he sees you, quickrestore and try again, this time crouch-strafing to the right after shooting him to avoid him seeing you. Sneak-shoot him in his new position, then quicksave again. Crouch-walk along the outer wall until you can see the feet of the marine who's standing past the second huge rock. Don't shoot him yet, but instead look for a marine a ways to the left, on the other side of the area. (It's the marine that you double-barrel on your way to the dark tunnel in the other attack strategy.)
When you can see him in his dark corner past the two short green plants, shoot him in the head for a one-shot kill. Crouch-walk up to the second huge rock without letting the marine behind it see you, then quicksave. Crouch-strafe very slowly to the right until you can see part of the marine's head, but he still can't see you. Shoot him in the head for a one-shot kill, then crouch-walk around to where you can see and head-shot the final marine. He'll be facing away from you, so it won't be hard to get into position to shoot him. (SRC: Due to increased object boundary clipping problems, you'll be unable to head-shot the first of those two marines. Also, the second one will probably be facing your way. You might just want to sneak-shoot them both with the pistol.)
After they're all down, search the tunnel carefully for supplies, then leave it and grab the marines' weapons. Look just to the right of the tunnel entrance for a small crouch-only passage that leads to a hidden spot with several health packs and some AR grenades. Watch out for the nearby tripmine, though. In the back of the marines' area, find the doorway that leads to a small room. In it, grab the crossbow ammo and use the valve wheel to open a storm drain hatch in another area.
Go back the way you came and through the rocky passage to return to the first outdoor area. Go to the edge of the ground and drop carefully onto the lower cement ledge, then jump across to the supply area you noticed but skipped earlier. After gathering up what you need, run across the gap so that you land on the ladder, then get back up onto the higher ground. Go over to the rock gap that you went through to get to the marines' area, then look to the left of it for another rocky passage that'll take you to section c2a5x.
Section c2a5x: FOUR-PART OUTDOOR AREA (LEFT HALF)
This next outdoor area has two hazards in it. One is a big tentacle beast like the ones you had to fry in the "Blast Pit" chapter. This one can't be killed, but there is some ammo near it to be collected. However, the first thing to do is go all around the perimeter of this area, killing headcrabs that are hiding in the sand. (SRC: The first thing to do is gauss-altfire-blast the chopper again.)
Have the crowbar out and ready, then crouch and start swinging at the top of a sand pile the moment it rises up. You should be able to kill the crab before it can crawl out of the sand and attack you. After the perimeter is secure, it's time to go for the ammo. Make noise in one spot so the tentacle will attack over that way, then crouch-walk over to a spot behind the tentacle. After quicksaving, run over to a nearby bit of ammo and grab it, then run for safety. Keep it up until you've gathered all the goodies from near the tentacle.
To the right from where you entered the area, there's a sandy slope with a dark rocky passage past it that you can crouch-walk through to reach the fourth and final outdoor area. This one has no enemies, but is covered with land mines. From next to the sign, turn left and move along to the end of the raised sandy ledge, then turn right and go forward to the cactus.
Past it is a small military supply area. Shoot the ground that's a bit to the right of the meshy netting with the assault rifle until a land mine explodes, then go under the netting to see if there are any supplies there. There should be if you never went back to section c2a5w after entering this section. (Doing that will make them disappear.) Past the netting, crouch-walk between two huge rocks and get up on some raised ground.
Go over to where an open storm drain is surrounded by barbed wire fencing. Get onto the bit of raised ground that's next to the back of the fence so you can jump over the fence and land on the back of the open hatch. Move around to where you can climb down the ladder in the shaft without falling and taking damage. At the bottom of the ladder, break through a grating and move down the tunnel to reach section c2a5a.
Section c2a5a: CLIFFSIDE MANEUVERINGS AND THE RPG
As you near the end of the tunnel, get the pistol out and move forward very slowly while looking to the right. There's a marine and a turret over that way on cliffside paths, and you'll want to take them down now. Get to where you can see the marine on a path that's way below you, and kill him with the pistol. Get out the crossbow and go into zoom mode, then strafe to where you can see the turret and quickly shoot it down.
SRC: The marine will probably run out of sight before you can kill him, so take down the turret, then sneak-shoot the marine mentioned below with the .357 before going to the other side of the ledge and finishing the first marine off with the pistol.
Get the pistol back out and drop down to the ledge below the pipe. Turn left and walk to the edge of the ledge, then look down and sneak-shoot the marine who's on a ledge a little below yours. After he's down, carefully drop to a small intermediate ledge, and then down to his. Get his gun, then drop down to the next ledge in the series. You'll take a bit of health damage, but you can enter a small cave by running over a rock, then look around to find two health packs and a bullet clip.
Crouch-jump back over the rock on its left side, then turn left. At the end of your ledge, look down and drop to one small ledge, and then to another one. Quicksave before the next drop, since it's onto a very narrow bit of ledge, and it's far too easy to fall off. Right after you land on it, strafe right to help stay on. (Or crouch-jump to the ledge instead of crouch-dropping to it. That might help you skip over the ledge's narrowest part.)
Crouch-walk along to find an armor battery, followed by a rickety wooden bridge. The two cables that the boards are setting on are sturdy, so crouch-walk along one of them. After you pass the marine you shot down earlier and turn a corner, look ahead with the flashlight on to see the feet of another marine who's standing behind the big metal structure that connects some huge pipes together. Sneak-shoot him with the pistol, then follow the ledge past him and to another corner.
Just past that corner is a supply cave with a marine standing near the cave mouth. Crouch-walk carefully to where you can shoot him in the foot with the .357, then quickly finish him off with another shot when he charges you. Go to the back of the supply cave and pick up the RPG and loose rockets. The newly resurrected Apache chopper will appear outside and start flying back and forth in front of the cave mouth. (SRC: The chopper may not appear until you go a short way past the cave.)
It's possible to trick it into damaging or even destroying itself with its own missiles, but that's kind of hard to accomplish. I did it several times in the original version of the game (and in version 220.127.116.11) by moving past the cave to get the chopper to see me (rather than activating it by going for the RPG). I moved back and strafed right a bit when it started shooting, then let it see me again in the cave mouth right before running to the back of the cave for cover. It then sometimes (but not always) fired missiles toward the cave mouth and damaged or destroyed itself. In game version 18.104.22.168, I found it to be much harder to get the chopper to destroy itself, but it will usually at least damage itself, making it easier to shoot down.
It only takes two (SRC: one) RPG rockets to destroy it, so you may just want to get rid of it that way. It's easiest to hit the chopper as it's flying right-to-left in front of the cave mouth. After the first rocket hit, retreat to the back of the cave and wait to see if the chopper will get lucky and hurt you with a missile strike. If it doesn't, quicksave. If two rocket hits don't destroy it, switch to the assault rifle to finish it off.
After it's down, search the supply cave for any other supplies, then start off along the cliffside path that leads on past the cave. When you come to a ladder, carefully crouch-walk over to where you're in front of it, then climb it to the top. Right past that, you'll have to crouch-walk up a "ramp" and then hop up a series of "stepping stone" ledges to reach the bottom of another ladder.
Climb it and move along until you approach the open end of a large pipe. There's a headcrab in that pipe, and the best way to get rid of it is to strafe in front of the pipe (while facing into it), then quickly strafe back out of the way so the headcrab will leap to its death. (It won't actually die, but it darn well should!) Enter the pipe and go along it until you reach section c2a5b.
Section c2a5b: TWO ENEMY TANKS
When you reach a path split in the pipes, turn right and go forward to where you can drop down into a watery alley-like area. Run forward to where you can jump-crouch into another pipe entrance, then turn right past it. Go to the end of the pipe, then climb up the ladder just far enough for a nearby marine to see you. Quickly climb back down, then go all the way along the pipe to its other end.
There's another ladder there that you can use for a quick peekaboo routine to get the nearby marines riled. Get back in the pipe and move down to the corner that's near the first ladder you went up. Wait there in safety while all the marines up above go nuts and throw grenades around everywhere, eventually killing themselves and blowing up their own tank!
Wait for the sounds of explosions and radio chatter to stop (or for you to get sick of waiting), then go up the ladder that you first went up to get to the area that's behind the tank. Use the assault rifle to blow up the tank's turret if it's still intact, then look around to see if there are any marines still alive.
SRC: Marines usually won't throw grenades unless they have line-of-sight with an enemy. You'll need to come up behind the tank and quickly kill the marine who's off to the left, then wait for the other marines to come around the tank after you. This can be very hard to survive. Try quickly killing the first marine with an AR grenade, then use rockets and/or AR grenades on the marines as they appear at the back of the tank. If they stop coming at any point, you can try to move into position to sneak-shoot the rest, but you'll probably be seen.
After the whole area is secure, look for supplies. In the area behind the tank, there's an ammo stash that includes rockets and C4 satchels, plus two small open garage rooms that have first aid stations and some other stuff in them. In the big area in front of the tank, you'll find lots of assault rifle clips and AR grenades next to the sandbag walls.
When you're ready to go, find the blinking red-and-green button in the small shed that's to the left of a large metal door. Use the button to open the door, then go through it and quicksave before you approach the corner. There's a rocket-firing tank ahead, and you'll want to sneak-shoot it. Get out the crossbow and go into zoom mode, then carefully round the corner to where you can see a bunch of crates ahead.
Move very slowly toward the crates until you can see the very top of the rocket tank's turret over the top of one of the crates. Don't move far enough forward for it to see you, or it'll start firing. If you mess up, quickrestore and try again to position yourself correctly. Once you're in the right spot, you can fire six darts into the tank's turret to get it to explode. (SRC: It'll take 12 darts, and you'll have to aim a bit above the turret to hit it.)
If you'd rather save the darts, there's a way to trick the tank into blowing up its own turret. Crouch-walk around the corner, then stay crouched as you move along next to the right wall, bashing crates that are in your way. After you bash the second one, move up to the explosive crate, then stand up and run by it on its right side. As soon as you're past it, turn left and run for the sandbag wall that's just to the left of the tank. Quickly crouch-walk in between the tank and the sandbag wall, then wait there for the tank to blow itself up. If its rockets aren't hurting it, adjust your position slightly until they are. Just be sure to stay crouched and behind the sandbag wall to avoid damage.
SRC: It's hard to squeeze in between the tank and the sandbag wall, and it won't fire while you're so close to it. However, you can go stand next to the tank in a spot that allows you to look up and bash on its turret with the crowbar. Do so until the turret blows up. You shouldn't be damaged by the explosion, but you might want to crouch down near the tank and shoot out its turret with the pistol, just to be sure. You can return to the first tank's area to resupply on bullets afterwards.
Bash all the non-explosive crates on the street to find supplies, including ten hand grenades, then walk up to the large hole in the wall that's near the tank. There are some marines in the lower area past the sloping sand bank, so toss five hand grenades through the wall hole so that they'll land near the marines. Next, jump-toss several snarks through the hole and wait a few seconds. Then jump through the hole and crouch-walk forward to the lower area with the assault rifle out.
Shoot down any surviving marines, then look around for supplies, which include five hand grenades to replace the ones you used. To get out of the lower area, go to the end of it that has a sandy slope that you can climb up. To get back through the wall hole, run up the wall piece that's leaning next to it, then jump through. Squeeze between the right side of the tank (your left) and a sandbag wall (or jump-crouch onto the sandbag wall), then move on to reach a large metal door that will slide up for you as you approach. Go through it and wait for it to close in order to reach section c2a5c.
Section c2a5c: GETTING INTO THE EXPLOSIVE-RIGGED BUILDING
Get out the assault rifle and wait for the second metal door to open for you, then move forward and up against the left wall. Look over to the right for a vortigaunt to appear, and quickly shoot him in the head when he does. As for the alien grunt that's over to the left, do a quicksave, then toss a hand grenade over to where he is without letting him see you. The combined explosion of the grenade and a couple of land mines should instantly kill him. If not, quickrestore and try again. (Or use an AR grenade to finish the job. Or try skipping the explosives and sneak-shooting him with the pistol.)
Don't go into the grunt's land mine area, but instead go past where the vort was to find an alley with a tripmine. There's no need to shoot out the tripmine since you can get onto the low end of the slanty rubble, run up to its high end, and jump over the tripmine from there. Move toward the steps ahead slowly while looking up, and back up quickly when some more cinderblock rubble starts to fall. If it hits you, you'll take a small bit of damage. As Burt Bacharach might sing if he were playing this game:
"Cinderblocks are falling on my head.
If they keep doing that, then soon I will be dead.
Then I'll throw a fit!
This game I'll frickin' quit!
Those cinderblocks are falling on my head, they keep falling."
Go down the steps and jump over the next tripmine, then quicksave. The following tripmine is at the bottom of some more steps, and it's a bit trickier to jump over, plus there's more damaging rubble rain just past it. To avoid that, jump over the tripmine laser's left end, then strafe left as soon as you're past the steps.
Run forward to the wall ahead and get out your hand grenades. Look up to see a sniper's nest, and lob a grenade into it. (You might want to quicksave first so you can quickrestore if you mess up. Also, try moving back from the wall just a bit before throwing the grenade.)
Grab the shotgun that's near the dead security guard, and ignore the tripmine on the right as you head for another small land mine area. You could shoot out the mines with the assault rifle or pistol, but all of them can be avoided. Start by hugging the left wall as you enter the minefield. Go straight forward until you reach the wall ahead, then turn left and hug that wall until you reach a corner. Stay next to that wall as you turn the corner and move to where you're directly underneath a sniper nest.
Get out the assault rifle, turn to where you're facing the wall and looking up at the sniper, then quicksave. What you want to do is back up to the barbed wire barricade, lob an AR grenade into the sniper's nest, then run forward to the wall again. If you do that fast enough, and don't accidentally hit the nearby land mine, you should be able to kill the sniper without getting hurt. If you mess up, quickrestore and try again until you get it right. (You might want to shoot out the land mine from the nearby corner first.)
Go to the right end of the barbed wire barricade and crouch-walk under it until you can see two explosive barrels ahead and to the left. Shoot them with the pistol until they explode, then move on past the barricade to where a large electrical structure has fallen against a building. Jump-crouch onto its base, then run up it to get onto the building's roof.
Explore the roof until you find a large grate-covered fan between two vent shaft structures. Jump onto the fan and go past it to find a large blackened hole in the roof. Look through the hole to see some large wooden crates. Do your best to crouch-drop through the hole and onto the crates to avoid damage (and to get to section c2a5d).
Section c2a5d: EXPLOSIVE-RIGGED BUILDING AND HORNET GUN
Bash all the crates in the room you drop into to find a health pack, then go through the door and turn left. Bash the crates there, then push through the partly open door and bash all the crates in its room to find an unset tripmine. Go back out into the hallway and start on the tedious, nerve-wracking journey through the heavily tripmined areas. (Note that no matter how remote a tripmine or explosive barrel may look, don't detonate it, or it'll blow up everything.)
Jump over the first tripmine from on the steps near it, then jump onto the railing near the second one. Quicksave before you try to run along the railing, since doing so often detonates the tripmine for no good reason. Either keep quickrestoring and trying again until you make it, or try jumping over the false detonation point.
Past that, push through the door on the left. You can bash the first two crates past the door, but that's all. In the back, push the smallest crate up against the next-smallest so you can jump-crouch onto the smallest one, and then crouch-walk onto the biggest one and then onto the big window's ledge. Drop carefully down to the floor below, then get out the pistol and shoot the two headcrabs you can see a ways ahead.
When you get to the corner past where you dropped down, turn right and go forward to find a large crate you can safely bash to get another unset tripmine. And now, it's time to go. The "regular" way out is more trouble than it's worth, so I'm going to share with you a tricky way that takes advantage of the fact that you can jump onto tripmines without blowing them up.
From the crate you just bashed, turn around and go over to the nearest tripmine, which is on the side of a wooden crate. After quicksaving, move up next to the tripmine and carefully jump-crouch onto it. You can then crouch-walk onto the crate it's attached to, crouch-jump to the nearby crate of the same size, jump-crouch onto the railing, and then drop onto the escape lift. If the jump to the railing is too hard, then instead jump over another tripmine beam to a nearby crate which is next to the railing. Once there, move up against the railing and jump-crouch over it. (SRC: You'll first need to drop down to the floor and push that last crate up against the railing.)
Once you're on the escape lift, move up against its button panel and use it to descend. After the lift stops, look for the hornet gun on the floor nearby. It's going to be a very useful weapon! Try it out by using its altfire mode to blow up the explosive crates in the room. Crowbar-bash the remaining crates, then collect the supplies.
Have the hornet gun out when you start down the winding corridor. Stop when you've got a clear shot at two explosive barrels ahead, and blow them up with altfire hornets as soon as the security guard runs by you. Run to the guard and talk to him to get him to follow you, then lead him to the corner that's to the right of the corridor entrance and leave him there.
Wait there with the assault rifle out in case any marines come into the room, then crouch-walk carefully over to the corridor entrance, firing hornets so that they'll go around the corner and hit any nearby marines. Keep going slowly down the corridor and doing that until you've confirmed that all of the marines are dead. If you haven't already hit the trigger point that loads section c2a5e, go down the corridor to get it done.
Section c2a5e: ANOTHER TANK, A WRECKED BUILDING, AND A HELIPAD
As soon as this section loads, turn around and go back to the previous section to pick up your security guard. Now return to this section and go to the back of the nearby truck. The fact that you went back and forth between sections like that should have eliminated the turret that was in the back of the truck. If not, get to where you can shoot it in the leg with the pistol. Jump into the truck and bash the crate to find some gauss gun ammo.
Move past the truck slowly until something ahead explodes, then get your security guard to wait there for you. You don't want him getting killed in the area ahead. Run up the large ramp that leads outside, then turn right and run up the smaller ramp. Hide near the wrecked door until a jet flies over and bombs some alien grunts out of existence, then get out your crossbow.
Crouch-walk up to the corner very slowly until you get to where you can sneak-shoot the turret of the tank that's a ways to the right without it firing at you. (SRC: More clipping problems here. Use the crates that are against the back ledge to get up on it. It's possible to sneak-shoot the tank from there, though you'll have to aim a bit above its turret to hit it. Or if you had a lot of patience, you could destroy the tank's turret with altfire hornets from there.)
After it's blown, you'll need to kill the two marines that are near it. You could sneak-shoot them around the corner or from up on the ledge with the hornet gun, but it's easier to let them see you and then shoot them down with the gauss gun while watching out for their hand grenades.
Break all of the nearby crates for health and armor, and go back to the truck you found gauss gun ammo in if you didn't pick it up earlier. Go down to the tank you destroyed, then turn right and go up to the start of a back alley. Before you enter it, find the sniper nest that's high up on one wall. Hang back to where he can't shoot you, and throw a hand grenade at him after quicksaving. Quickrestore and try again if you miss, then enter the alley and wait for a bombing to happen. (Don't worry -- it can't hurt you.)
Find the only open door in the alley, then get out the .357. Crouch-walk carefully up to the open door, looking to the left for a marine that you can sneak-shoot. He'll run toward you after you hit him once, so shoot him again the instant he runs into view so he won't have time to alert his comrade. Go through the door and sneak carefully up to the corner, looking to the right for the next sneak-shooting victim.
After they're both down, bash the crates in their area for an armor battery, then head up the stairs. At the other end of the upper floor area is a security guard and a locked door that leads to the most incredible supply area in the entire game. Get the guard to follow you, then go over and stand near the door until he unlocks it for you. (If the guard got killed somehow, go back and get the guard you left at the bottom of the big ramp. He can open this door, too.)
In the supply room, find the light switch and use it to turn the lights on, then run along next to both rows of shelves to see what all you can pick up. Also, bash the crates in the back for a few extra goodies. What a place! Even the storage building at the dam in Half-Life 2 isn't this great!
When you're done there, go over to the big window that's near the top of the stairs. Crouch-jump onto the window's sill, then crouch-walk onto the narrow ledge that's just beyond it. Move along the ledge until you come to where you can get onto the top of a large light-green machine. Jump from there to the other light-green machine, then take a running jump at the broken fire escape's lowest ladder. Climb it to get onto the fire escape, then climb its other ladder to get onto the nearby roof.
You could cross to the other side of the roof, then set two laser tripmines carefully on the short wall so that you could use them as stepping stones to get onto the wall. You could then fall (painfully) into the helipad area, use the crowbar to bash through the large doors on the other side, and then run onwards to section c2a5f. This extreme shortcut isn't recommended, and the rest of this section's walkthrough will assume that you don't take it. (SRC: This shortcut will be impossible to take.)
After getting onto the roof, cross to its other side, then slowly crouch-walk up to the jagged edge. Look down to see an unsuspecting marine on the floor below. Get out your crossbow and use its zoom mode to deliver a fatal head shot to the marine. Find the large slanty beam that leads from the roof all the way down to the floor and get on it. Crouch-walk slowly down to where you can see another marine through a doorway that's ahead and to the left. Use zoom mode to deal him a fatal dart to the head, too. (SRC: It seems to be impossible to one-shot-kill these marines, so quickly two-shot them before they can alert the others.)
Go down to the bottom of the slanty beam and turn around, then move slowly toward a doorway with a light on a pillar past it. The final marine of the area is past the doorway and on the right. Sneak up to where you can sneak-shoot him with the .357, then check the area past him to find several health packs. Go back to the base of the slanty beam, but don't go up it yet. Look around near it for a door you can push open to return to the alley. (SRC: For some reason, the guard from the building across the alley will be standing there, even if you left him somewhere else. What is he, psychic or something?)
You can now get back up onto the roof by using the slanty beam or by doing it the way you did it the first time. The slanty beam is faster, but a bit more dangerous, since it's hard to jump from its top to the roof without falling and taking severe damage. You could, of course, quicksave and keep trying until you make it. (Or try to crouch-walk from the beam to the roof.)
Once you're back on the roof, stand next to the top of the slanty beam, but don't get on it. Instead, look past it and to the right to see the small top of a broken wall that you can take a running jump to. Once you're on it, drop down onto the floor piece just past it. Or instead of that, crouch-walk down the slanty broken wall that's just to the left of the big slanty beam, then jump to the floor piece. Either way, move to the floor piece's other end, where you can walk along a small metal beam to another floor piece. From there, it's easy to take a running jump to the floor piece next to the doorway that you need to go through.
Go down the short hall to another doorway, but don't go through it yet. Instead, stop near it so that you can clearly see some large doors on the other side of the helipad area that have red STOP signs on either side of them. Get out the hornet gun and quicksave, then fire exactly 55 (SRC: 130) altfire hornets at those doors. If you do it right, they'll be almost ready to blow up, but not quite. Quickrestore and try again if you accidentally destroy them, and quicksave if you don't. (SRC: Put a tripmine on the wall to the right of the doorway, fairly high up. Don't forget to duck under it on the way out and back in!)
Keep the hornet gun out and run through the doorway backwards. What you want to do is back up toward the center of the marked-off helipad area until you hear an explosion behind you, then immediately run forward to the doorway you came through. Stop just past it and turn around, then quickly use altfire hornets to finish the job of destroying the big doors you were shooting earlier.
As soon as they blow up, turn and run down the hall, then drop onto the floor past the doorway. Run for the big slanty beam and use it to get back on the roof, then stay there and watch as the osprey plane drops off marines two at a time to fight the alien grunts who came in through the destroyed doors. (Note that the marines might shoot at you if you're too far back on the roof, so stay near the top of the slanty beam.)
Every time the osprey stops to hover and drop marines, quicksave, then hit it with altfire hornets until it starts circling again. Once you destroy it, quickrestore and hit it with almost (but not quite enough) altfire hornets to destroy it again. Wait until it starts flying directly over your roof instead of hovering and dropping marines, then finish it off with the pistol while it's not directly overhead. (SRC: It won't fly over you, but it will fly by without dropping any marines off. Right after it does, finish it off with altfire hornets.)
After the osprey is toast, get back out to the helipad area like you did before. (SRC: Watch out for an alien grunt in the hallway that leads to the helipad. Even if your tripmine got one, there may be another one in there. Try to sneak-shoot it with hornets or the pistol.) Quickly shoot down any surviving marines, preferably from the hallway leading to the helipad with the hornet gun.
You can then go through the big doors you blew up with the hornet gun to get to section c2a5f, but once again, I don't advise that since you'll be passing up another nice supply room. Find the other big doorway to the right of the one you horneted, then go through it and down the ramp to the locked supply room door. There's an alien grunt nearby (unless the marines found it and killed it), so take it down quickly with RPG rockets.
Go past the grunt and locked door to reach a door you can open to return to the alley. (SRC: That psychic guard will be standing there again!) Go into the building on the left and back up to the supreme supply room. See what all you need from it now, then get the security guard to follow you all the way to the other supply room's locked door. After he opens it, go inside and get all the goodies (and use the first aid and HEV stations if you need to), then go back and get your other security guard if he's still alive. Return to the second supply room and have that guard follow you, then go through the big doors you horneted open earlier and on to where section c2a5f loads.
Section c2a5f: MEGA-VORT AREA, GARAGE TRAP, BOMB-IN-A-PIPE, AND MUCH MORE
Get out the hornet gun and go up to the corner where the big hallway turns left. Around that corner is an area where dozens of vortigaunts will teleport in a few at a time. Don't run for the mounted gun you can see near them, but instead move to where your security guard(s) will see the vorts and start shooting, then run back for cover before you get zapped.
After your guard(s) get killed, stay at the corner and shoot hornets from there, ducking for cover whenever you see a vort charging up. You should be able to kill most of them before they can reach your corner, but be ready to quickly switch to the assault rifle or shotgun if any of them make it that far. When it looks like all the vorts are dead, move past the corner cautiously, since there may still be some up there.
SRC: The vorts run back to your position a lot faster, making it much harder to kill them all unzapped. It may be better to position your guard(s) a ways back from the corner for backup fire support before you start horneting the vorts. Also, bring out the assault rifle and then the hornet gun so you can hit the "Last weapon used" key to quickly switch between them. Another thing you can try is moving slowly up to the corner until you can barely see around it, then firing off a bunch of hornets to sneak-shoot the vorts. That would be particularly useful with the starting crowd.
After they're all dead for sure, look near the mounted gun for health and bullets, then use the weird alien whoosh-thing on the ground to get up to the higher floor. The best way to do that is to run at the whoosh-thing while facing the way you want it to blow you, then jump as soon as you're on it. Once you make it, turn right and crouch-walk forward until you hear the sounds of marines and aliens fighting in the lower area that's just ahead.
Wait for the sounds to stop, then get out the hornet gun and see if you can sneak-shoot any of the survivors without being seen. Use the assault rifle if necessary to finish the last ones off, then turn and drop back down to the lower floor with the whoosh-thing on it. This is your last chance to go back and get stuff from the two guard-opened supply rooms, so go do that. Return and use the whoosh-thing to get back onto the upper floor, then look down into the lower area where the guys were fighting earlier. If the vent shaft entrance that's next to the ground near the back right corner is still covered by a grating, shoot it with altfire hornets until it breaks. If any snarks run out of the shaft, wait until they time out and explode before dropping down.
NOTES: It's possible to use tripmine "stepping stones" to get back to the upper floor (SRC: Not!) so you could return to the supply rooms later on, but that's not worth the trouble. Also note that the only way to get onto the top crate that has a health pack on it (other than using tripmine "stepping stones") is to jump to it from on the upper floor. You can get to the health packs on the two lower crates by taking a running jump from on the nearby cement chunk.
Go over to the vent shaft entrance and crouch down. Use the flashlight to help you see the shaft's back wall, then shoot it with altfire hornets until it breaks. That released a bunch more snarks, so quickly run and hide on the other side of the health pack crates. Wait until you haven't heard snark noises or explosions for awhile, then return to the vent shaft. Move along it until you reach the broken-open area, then go into it to pick up some snarks that you can use. Keep going down the shaft past that until you come to a grating blocking your way.
Bash the grating with the crowbar, then turn and go back around the corner while marines shoot out a large part of the shaft. Get out your snarks, then quicksave. Turn the corner and toss several snarks through the shaft opening so they'll attack the marines in the room below. Snarks are sometimes a bit funny about when they let you throw them, so quickrestore and try again if you have to. When you're sure all the marines below are dead, go back to the snark stash to resupply.
To drop down into the garage area without taking damage, carefully crouch-drop onto the back fender of the raised car, and then to the floor. Or just drop and take damage, then use the first aid station on one wall to heal up. There are also three armor batteries that you can take if you need them.
Go over to the garage's small door and push it open, then quickly retreat all the way to the other side of the garage as some marines blow up the doorway and cover it with rubble. (You could quickly push forward past the doorway right after opening it, jump-crouching over an explosive crate and running forward to the big gun before the explosions happen, but you'll get way more damaged that way. SRC: The door opens very glitchily, so move out of its way and then go past it.)
After the explosions rip a big hole in the wall to the left of the door, do a quicksave, then get out your snarks and start jump-tossing them through the hole. The marines outside may start firing AR grenades through the hole, but if you're close to it, the grenades should go over your head and not hurt you at all. An alternative to jump-throwing snarks through the hole is jump-shooting hornets through it. Also, you can fire hornets through the debris holes past the small door.
SRC: Neither the hornets nor the snarks work very well, and you may find it impossible to kill both marines with them. If so, see if you can shoot a marine through the debris holes with the pistol. After that, use the method below to elevate yourself, then quickly hit any survivors with RPG rockets.
When you're sure both marines are dead, use the two hanging control switches in the middle of the garage to see which one works the empty lift. After it's lowered, hit its control again and run onto it before it can rise up. The best way to get through the wall hole is to run to it from on the raised lift without trying to jump.
In the outdoor area, go over to the huge gun emplacement and use it to blast the nearby metal door to pieces. Keep shooting at the doorway until alien grunts stop appearing, then go through the doorway and down to where you can look into a room where marines are fighting aliens. Use the hornet gun's altfire mode to quickly kill the vort that's across the room on the same walkway you're on, then retreat out of sight.
When the sounds of fighting stop, quicksave before you go back to where you can see into the room below. There's probably an alien grunt or two still alive, and you're going to want to sneak-shoot them with something if you can. Otherwise, quickly roast them with the gauss gun. If you can't see them at first, they're probably in the side room below the walkway. Go along the walkway until you find a ladder you can climb down, then go kill the grunts.
After they're dead, check the side room for stuff you need, not neglecting to crouch-walk into the open metal crate to find gauss gun ammo. Climb back up the ladder to get back onto the walkway, then jump onto the railing before you try to jump over the big walkway gap. Past the end of the walkway, turn left to find a first aid station, then go around the corner and slowly forward until a grunt throws a marine through a wall.
Move to where you can sneak-shoot the grunt through the wall hole with hornets, and be ready to quickly switch to the crossbow or gauss gun to finish him off if he runs into sight. Go stand in the doorway to the right of the wall hole and look to the left to see a large floor hole. There are two marines just below that hole, so shoot hornets at the hole until they stop swerving downward.
Go over to the big wall hole that's past the floor hole and look down to the ground below to see a marine fighting an alien grunt. Immediately start firing hornets at the grunt, who will easily beat the marine. Take down that grunt as quickly as you can, then use altfire hornets to kill the marine that you can see on a rooftop a ways past the grunt. (SRC: The rooftop marine is your first target, since he'll be shooting at you. You may prefer to use the crossbow on him.)
Look up and fire some hornets at the ceiling directly above you, and you may be able to score some hits on a grunt up there before he moves. After that, go to the edge of the big floor hole you horneted the marines through and completely destroy the biggest wooden crate down there with altfire hornets. Carefully crouch-drop down onto the nearest small crate, then bash all three crates to find a health pack to make up for any falling damage you took.
Find the big ramp nearby that leads up to two short sandbag walls. Don't go up the ramp right away, though. First, go down the narrow "alley" to its left with the shotgun out, ready to double-barrel the vortigaunt that's hiding around the corner. (SRC: This vort probably ran out and joined the marine-vs.-grunt battle earlier.) After it's dead, go up the big ramp, then turn around and look back the way you came.
You should be able to see and hornet-shoot the high-up alien grunt that you started shooting through a ceiling before you dropped down. If you can't see the grunt right away, move on a ways past the top of the ramp and jump up and down to get its attention. (If it starts firing hornets at you before you can kill it, you may want to try horneting it from near the base of the building it's on or next to the vort's little hideaway rather than going up the ramp.)
Go back down the ramp and turn right. Go past an alien whoosh-thing on the ground and on to a small security booth. You can't open the booth's side door, but you can pick up a shotgun from a shelf. Return to the whoosh-thing and use it to get up onto the nearby rooftop. Try to land on the large square vent thing to avoid taking any health damage. (SRC: It's impossible to land on the vent.)
Near the vent thing is a grating that you can bash and drop through. Crouch-hop out of the water and into a large metal pipe, then get out the crossbow and quicksave. Go into zoom mode and move down the pipe with your sights aimed just a bit to the right of the center of the round hatch door that's ahead. When a marine opens that door, quickly shoot him in the head for a one-shot kill. If you miss, quickrestore and try again. (SRC: You'll probably have to hit him with two quick darts.)
As soon as the marine is dead, leave zoom mode and start moving backwards. The bomb he put in the pipe is about to go off, and you'll want to be crouching down at the bottom of the water when the flames go by overhead. As soon as they disperse, crouch-hop back into the pipe and go to its other end. Push open the hatch door and drop into the room beyond. (SRC: Hit the "Use item" key to open the hatch door.) If you've already killed the marine like I said to, you won't have to worry about him attacking you now.
Go around the corner that leads to another room, then retreat until the sounds of marines fighting headcrabs stop. Get out the hornet gun and go into their room slowly, trying to sneak-shoot the survivors with hornets. If there are marines alive in there, you might want to switch to the assault rifle to finish them off. When you reach a ladder that goes down to their floor, use it and go check the alcove near the first aid station to make sure no one is hiding in or near it.
From a spot on the walkway near the top of the ladder, jump onto the railing and then onto the skinny bit of pipe that leads to a large hatch door. Use the door's wheel to open it, which will probably cause you to be knocked off the pipe. That's okay, since that won't hurt you, and you can climb back up the ladder and jump over to the pipe again.
Crouch-walk through the open hatch door, then go up a short ladder and along the large pipe until you reach its other end. As you near it, get out the .357 and carefully edge over to where you can shoot the marine who's next to the bottom of the stairs over to the right. He may see you before you can fire, so shoot him down quickly. If you manage to sneak-shoot him and he runs by you, quickly exit the pipe and finish him off before he can get upstairs and kill an essential security guard.
After he's down, go to the bottom of the stairs to find a room with a locked door and another marine who's hiding behind some shelves. Sneak-shoot him with the .357 if you need to use the first aid station near him, then go to the top of the stairs to find the security guard. After he holsters his gun, get him to follow you to the locked door. After he unlocks it, leave him there and go down the winding hallway past the door.
You'll end up behind the short sandbag walls that are near the large ramp you found earlier. There are two new vorts near the bottom of the ramp, so get out the hornet gun and horn in on them. Move up next to the second sandbag wall and shoot hornets over it. They should swerve down and hit the vorts, who will start running around. If they see you, duck down behind the sandbag wall for cover when they try to zap you. If they hide, look for them in the side niche next to the ramp where you blew away a vort earlier.
Now it's safe to go back and get the security guard to follow you again. Lead him down the big ramp and past the whoosh-thing to the little security booth. After he opens the booth's side door, get him to follow you again. Quicksave, then go through the door and down the winding corridor to where section c2a5g loads.
Section c2a5g: PARKING GARAGE GARGANTUA AND MILITARY TARGETING SYSTEM
As soon as this section loads, start running. When you exit to the parking garage, turn right and keep running without slowing or stopping. If you make it outside fast enough, the gargantua probably won't ever come outside after you. To confirm this, turn around as soon as you make it outside and go back to where you can see the gargantua in the distance.
It should still be standing behind a parked car, and your security guard will probably be shooting at it. If this is the case, turn around and go back outside, secure in the knowledge that the gargantua can't follow you out there. If that's not the case, restore the quicksave you made right before entering this section and try again. If you're fast enough and never get snagged, it should work for you eventually. Note that returning to check on the gargantua might free it up to follow you when it otherwise wouldn't, so try skipping that step if nothing else works. (SRC: There's no way to leave the gargantua behind, so you'll have to either blast it or work fast. See the two SRC notes below.)
Once you're outside, find the alien whoosh-thing on the ground and use it to jump over the wall and fall into a water tank. Jump onto the edge of the tank, then crouch-walk carefully along the narrow pipe that goes up to a point near the top of a waste silo. Jump-crouch onto the silo's top to find several health packs and a military targeting system that can be used to call for missile strikes in this area.
Use the targeting system's two levers to target the large doors you can see in the very back left corner of the area (top left on the targeting map), then use the central button to call the missile strike. Once those doors are blown up, you're through with the targeting gadget. Sure, you're supposed to use it to make yourself a way to get to those doors, but that's much harder than the method described in the next paragraph. (SRC: Jump ahead to the next SRC note to learn what you'll have to do instead.)
Drop carefully onto the slanty pipe and use it to return to the small water tank's edge. (Or take a running jump over the pipe and into the water, then hop up onto the tank's edge.) Move along the edge until you're next to the wall, then jump-crouch onto the wall. Turn right and go along the wall and across the big gate until you reach the slanty part of the area's outer wall. Jump onto the bottom part of the slant, then move along it until you can drop down onto the slanty bit of concrete that's on the left side of the blown-open doors. Quickly drop to the ground and run through the doors before the air strikes start up.
SRC: After you blow open the doors in the back of the area, you can either reset the targeting gadget to aim at the gate that the gargantua will break through (so you can blow it up when it shows up), or you can just quickly blast the other two things you need to in order to escape (leaving the gargantua behind). The other two things are the wall to the right of the blown-open doors and the two large electrical boxes to the right of that, next to what looks like a small radio tower. That last target is the hardest one to hit just right. You'll know you've got it when the radio tower falls over. Use the concrete ramps that start next to the silo to get down to where you can jump onto the fallen radio tower, then run across it and jump over to where you can run through the blown-open doors.
Run down the large tunnel until you turn a corner and find some side stairs to go up. Go around the corner past them to finally finish this looooong chapter and start on "Forget About Freeman!"
"FORGET ABOUT FREEMAN!"
Section c3a1: USEFUL CEILING TURRET AND SNARK PODS
In the room ahead, run through the gap in the railing on the right, then run down next to the spot where the first large chunk of ceiling falls down. Jump (SRC: jump-crouch) onto the narrow ledge next to that chunk, then jump-crouch onto it and crouch-walk over it. Move into the large control room beyond to be safe from the falling rubble.
After all the shaking around stops, jump-crouch into one of the large windows, then move forward to drop into the area beyond. Turn right and find the red railing. Practice running up to the railing and jumping over it until you can do so quickly and easily. (SRC: Jump-crouch onto the railing's ledge, then jump-crouch onto the railing.) That's your way back into the control room after you get the attention of the aliens in the area ahead.
Bash the crate next to the security guard to find a health pack, then get the guard to follow you. Go over to the right side of the large opening that leads into the big room with the crates in it, then get out the crossbow. Crouch-walk forward to where you can sneak-shoot the alien grunt that's around the corner and to the right of the wooden crates. Kill him quickly, before he has a chance to run around or see you.
Back off a bit and use the hornet gun to destroy all of the wooden crates. As soon as the vort that was hiding behind the crates sees you, turn and run for the railing. Jump over it, then turn right and run into the control room and crouch down. Stay crouched as you move over to the switch on the wall (or the keyboard on the table) and use it to activate the nearby ceiling turret.
If the turret can't see any of the aliens, fire some hornets through the windows while crouched near the turret controls to see if you can hit any of them. (Note that the turret will fire at your hornets, which will keep it alert.) After the first aliens go down, some more will teleport in within range of the turret.
It should be able to kill a few of them before it gets destroyed. Use hornets to finish off the rest, crouching for cover to avoid return fire. If firing hornets through the windows isn't working very well, try crouch-walking over to the doorway and firing hornets through the left end of the red railing. Be careful to not let any alien grunts see you. (The same goes for the turret if it hasn't been destroyed yet.)
When you think you've got everything, turn the turret off if it wasn't destroyed, then go up to the control room's windows slowly, ready to shoot any remaining aliens. There probably won't be any, so jump-crouch through a window (or jump over the railing) and go find the gauss gun ammo that was in one of the wooden crates you horneted to pieces. (Note that there might still be an alien grunt behind the green crates to the left of the big ramp. If so, get to where you can sneak-shoot him with the crossbow.)
Go down the big ramp, then turn right. Move up to where you can use altfire hornets to destroy an explosive crate, then fire a bunch of regular hornets so they'll go around the corner and hit the vorts in the next room. You should be able to kill both of the vorts that are in the open that way. As for the one that's hiding to the left, near the bottom of some steps, you can try to hornet it before it sees you, or you can just charge it with the shotgun or assault rifle.
Stand to where you can use altfire hornets to shoot the glowing snark pod that's over a hatch past the walkway. As soon as it breaks open, run for the base of the big ramp and wait there until you stop hearing snark noises. Now use altfire hornets to destroy the snark pod that's down the path to the left of the ramp, then run over to the hatch where the first snark pod was to wait these snarks out.
After they've all self-destructed, go past where they were to find a vine-covered side area with some stairs. Bash all of the vines out of the way, then destroy the snark pod at the top of the stairs and make a mad dash for the safe hatch area. Wait for those snarks to time out, then go back up the stairs to find that you can now reach an upper walkway with a first aid station. (You could have jumped over that walkway's railing from on top of the nearby green crate stacks, but that's a bit harder than dealing with the snarks.)
Go back down the stairs and look to the left to find some more vines to bash through. When you uncover another snark pod, don't destroy it right away. Instead, use altfire hornets to bash through some vines that are past it, then use them to blow up a stack of explosive crates. The explosion will bust the pod open, so run for your safe spot at the hatch while waiting for those snarks to time out.
Past the blown-up crates is one last snark pod near a ramp leading down. Use the usual routine of hitting it with altfire hornets and running for the hatch, then return and check out the fenced-in side room that's near the top of the ramp. Push the room's fence door open, then go inside to find an RPG and a spare rocket next to a dead marine. Use the hornet gun's altfire mode to kill the barnacle that's hanging in one corner before getting the snark pack that's under it.
Go down the nearby ramp and look into the room beyond it. Use altfire hornets to destroy the rightmost wooden crate that you can see near the other side of the room. Doing so will allow you to see the shoulder of the alien grunt who's behind the crates. Shoot some regular-fire hornets a bit to the right of the crates so they'll swerve into the grunt. When it starts moving, strafe left to where you're partway up the ramp so it won't be able to see you. You should still be able to shoot it around the corner with hornets, so do that until it's dead.
Crouch-walk past the left side of the two nearby green crates, then turn right and go over toward the alien whoosh-thing. The other grunt in the area is behind the large stack of green crates, so get to where you can see part of it. Horneting it would be too much trouble, so quicksave and blast it carefully with two RPG rockets. If you take damage, quickrestore and try again after backing up a bit. As soon as that grunt dies, another grunt will teleport in near the bottom of the ramp. Edge over to where you can sneak-shoot it to death with hornets.
Get out the crowbar and bash open the rest of the wooden crates in the room to find some supplies, then use the whoosh-thing to get up onto a narrow ledge with snarks and a health pack. From there, turn to face the top of the green crate stack, and run forward to drop onto it (don't try to jump). After getting the crossbow and gauss gun ammo, drop down to the floor and go back up the ramp to the fenced-in side room to resupply on RPG rockets. After that, go all the way back to the hatch you found earlier.
If you want to, you can go diving in the water near the hatch to find a dead marine with an armor battery, two assault rifle clips, and some AR grenades near him. However, you shouldn't need any of that, and there are a lot of zappy little leech worms in the water, so it's probably best to skip that. Use the wheel to open the hatch, then climb down the ladder to reach section c3a1a.
Section c3a1a: CANALS, ICHTHYOSAUR POOL, AND ENEMY TANK
When you get to where you can see a headcrab through the ladder, get out the pistol and shoot it to death. After you get off the ladder, go through the red laser alert, then quickly move to where you can only see the leg of the turret ahead. After it finishes shooting the headcrab that's near it, shoot it down with the pistol.
While standing near the fallen turret, use hornet gun altfire to destroy the two wooden crates you see ahead, and to shove around the metal crate. Doing so will reveal two headcrabs that you can kill with hornets. After they're dead, look down the two canals labeled "WEST" to see barnacles that you can alfire-hornet to death.
Push the metal crate into either canal, then push it up to the fence that's under the "WEST" sign. Use the crate to get over the fence, then check under both dead barnacles for health and armor. Move down to where you can get out of the water, hornet-shooting the nearby headcrab before you do. Around the corner past the headcrab, you'll find yourself standing next to a large pool that has an ichthyosaur in it.
Fire hornets into the pool continuously until you don't hear the ichthyosaur yell or moan in pain for awhile. Quicksave just in case, then dive into the pool and see if the big fish is dead. If not, quickrestore and fire some more hornets into the pool. After it's dead, you can swim to the back end of the pool to find two sets of hand grenades on the floor near the fence.
And now for another handy tripmine shortcut. Quicksave in case you mess up, then set a tripmine at about water level on the wall next to the left end of the pool's back fence. After the mine is set, you can jump onto it, then onto the fence. Edge along the fence carefully until you can drop into the water on its other side. (In earlier versions of the game, I could never get up onto a water-level tripmine, and ended up having to set two of them -- one a bit below water level, and one a bit above.)
Now I'll describe the "regular" way to get to the other side of that fence, since it includes a secret area (and since Source version players can't use the tripmine shortcut). Go down the ichthyosaur pool's side passage. After it turns right, crouch down and move through the large slow-moving cogwheel, then go under the double pipes and between the next two pipes. Turn right just past them and jump up onto the small ledge. (Note that this jump can be a bit tricky to do, especially without taking any steam damage.) Bash the padlock on the door with the crowbar, then check the room past it for a health pack and an HEV station. Go back to the ledge and jump onto the set of steam pipes over to the right, then move along them to where you can jump past the left side of the nearby barnacle. While avoiding the zappy little leeches, crouch-walk your way past the next large cogwheel on either side (or time your way under it if you can't squeeze past it on either side).
While bobbing on the surface of the water, use the RPG to blow away the turret you see near the sandbag wall, then get up onto the floor on the right side of that wall. Crouch-jump onto the wall, then edge over to where you can use the hornet gun to sneak-shoot the marine who's standing a ways to the right of the ladder.
After he's dead, restock on RPG rockets before climbing up the ladder. At the ladder top, turn right and start firing hornets at the opening between two huge rocks. Keep firing until the hornets stop swerving left or right, and you'll know the two marines hiding behind those rocks are dead. (SRC: You may have to get off the ladder and crouch-walk slowly toward the rock gap to get into a better horneting position.)
However, the tank that's behind the left rock isn't dead, so get off the ladder and very slowly strafe to the left so that you can see the tank's turret, but it can't shoot you. You could blow up the turret with altfire hornets, but that would take a long time. You might as well use RPG rockets, then go back down the ladder to resupply.
After the tank is destroyed, look for hand grenades in a dark niche a bit to the right of it, then crouch-walk along its right side (your left). Jump over a short obstruction when you come to it, then move up to the partly open door. Get the pistol out and sneak-shoot the turret that's just past the door on the left, then use the first aid station on the opposite wall if you need to. To get to section c3a1b, use the button on the back wall to summon an elevator, then get in and use its button to get it going.
Section c3a1b: REPAIR BAY WITH USABLE TANK
Move forward from the elevator and jump over the two narrow streams of green toxic goo that cross the floor ahead of you. I've found that careful crouch-jumps work best for this. (SRC: You might need a regular jump for the second one.) Turn right past the second green stream and go over to where you're standing near the wall, next to a green pool. Look past the pool to see the bottom of some stairs and part of a railing on the floor they lead up to.
Get to where you can barely see part of the marine who's next to the railing, then fire an RPG rocket at him, hopefully killing him. (SRC: Use altfire hornets instead.) Switch to the assault rifle and shoot down the other marine if he comes down the stairs after you. If he doesn't, crouch-walk over and sneak-shoot him with the hornet gun. Pick up the marines' dropped weapons, then go up the stairs and over to where you can see into a large repair bay.
Wait out of sight for the marines and alien grunts to finish fighting, then crouch-walk slowly over to where you can see into the bay. Get out the hornet gun and use it to take down any survivors. It's useful to note that they can't see or shoot through the metal walkway, so if you shoot one of them and he starts running around, quickly crouch and back up to where he can't see you, but you can see him through the walkway. Keep firing hornets over the walkway, and they should swerve down to hit your target. (SRC: They can see you and shoot you through the walkway, so stay farther back while horneting them.)
After the bay is clear, drop down to its floor and bash all the wooden crates to find supplies, including tripmines to replace the one(s) you may have used for a recent shortcut. The next thing you need to do is fire the tank's cannon to destroy the large door that's directly ahead of it, but doing so will cause several alien grunts and vortigaunts to teleport in.
The best way to handle this tricky situation is to get up on the side of the tank just a bit above its little ladder, then quicksave. Fire the cannon, then immediately back up to where you're against the nearby wall. Turn right and run along the wall until you reach the walkway's ladder, then climb it quickly. Run all the way past the bottom of the stairs in the previous room before you stop.
Wait for a bit, then crouch-walk back to the repair bay's entrance and use the same sneaky hornet strategy against the aliens as you did right after the alien-vs.-marines battle. If any alien grunts start firing hornets, run back past the bottom of the stairs and wait for a few seconds before returning. (SRC: Vorts can't zap you through the walkway.)
ALTERNATIVE: Crouch down right behind the tank's open hatch so that none of the aliens can see you when they teleport in. Fire the cannon, then look left and use the machine gun without changing position. You won't be able to see where you're shooting, but you should be able to spray the teleport-in alien group with bullets. Watch for vorts and grunts running around in the area to your left. Try to shoot them down before they can get to where you can't hit them with the machine gun.
SRC: Instead of using the machine gun, slowly and carefully back up to where you fall to the floor behind the tank. Make sure none of the alien grunts see you as you go. If a vort sees you, wait with the assault rifle out for it to come after you. Move back against the wall and jump-fire hornets over the tank until you're sure you've killed the two alien grunts. Try to get all the vorts, too, then peek around the left side of the tank to see if you missed any. (There's likely to be one behind the red tool cabinets.)
After you get them all, drop down and go toward the door you blasted with the tank. Stay on the right side of the passage, and slowly crouch-walk forward while looking left until you see part of the base of the weird ray gun that the grunts have set up. Fire lots of regular-type hornets toward that gun to kill the two grunts that are behind it. (SRC: Destroy the ray gun as specified below before horneting the grunts.)
Get out the crossbow and very slowly crouch-strafe to where you can see part of the ray gun, but it can't target you. Shoot it with darts until it goes poof, then turn to deal with the final alien grunt. It's over to the right, so get to where you can sneak-shoot it with the crossbow until it's dead.
Turn back toward the destroyed ray gun and run toward it. It'll somehow still cause a wall to collapse, and you don't want to be under it when it falls. (Stupid unconditional scripted event!) Before you go past the ray gun to find the exit door, there's one health pack and two armor batteries that you might want to go for.
Return to the repair bay and climb up its walkway ladder. Go back down to the bottom of the stairs, then move forward and left to find a large yellow machine. There's a big wooden crate near the machine that you can bash for a health pack, and there's an armor battery at the back of the narrow, dark passage that's on the right side of the machine. (SRC: There's no armor battery there.)
For the other armor battery, you've got to go back to the big toxic waste spill near the elevator. Crouch-walk carefully along the safe path between green waste until you get near another large yellow machine. Get to the machine's right side by making an easy jump over some toxic waste, then crouch-walk very carefully onto the machine's narrow rim. You can use it to cross over to the machine's left side (where the armor battery is), and then to return to the machine's right side. Once there, make the same easy jump over the toxic waste, then crouch-walk your way back to the safe area past the waste.
Go back to the repair bay, then go past the ray gun emplacement to find a large door with a button panel on the wall to the left of it. Use that panel to open the door, then go past it and use the big yellow button on the left wall. Soon after you do that, the "Lambda Core" chapter will start.
Section c3a2e: BIG LIFT AND ASSASSIN ROOM
Go through the big doorway and up some steps on the right. Enter the small control booth and use its button, then run over to the big lift platform with the truck on it. Stay toward the back on the right side of the platform as it descends to a room that's far below. When it stops moving, use the hornet gun's altfire to shove the nearby small wooden crate aside so you can hornet-kill a headcrab. (SRC: The crate won't move, so destroy it with altfire hornets to get at the crab.)
Destroy that crate with alfire hornets if you haven't already, then get out the crossbow and edge carefully over to where you can sneak-shoot a bullsquid that's spitting gook at a headcrab that's on top of some crates. After the squid is dead, use the hornet gun to kill the three crate-top headcrabs, then look behind the nearest stack of green crates to find one last headcrab to hornet.
SRC: Stay back on the lift and hornet-kill the three crate-top headcrabs from there, plus any floor-level headcrabs that come within range. If the bullsquid runs into view, quickly kill it with the assault rifle or shotgun. If not, sneak-shoot it with the crossbow. After it's dead, look around for more floor-level headcrabs if you only killed one or two before.
Use the crowbar to bash all the wooden crates in the area for supplies, then use the yellow ladder in one corner to climb up to where you can access a first aid station and pick up some shotgun shells and hand grenades.
Go through the door past the grenades, then climb down another yellow ladder and go through another door. Get out the crossbow and quicksave as soon as you're through that last door, since there are more of those super-quick female assassins in the large room ahead. Crouch-walk slowly straight forward from the door until you come to a spot with a small fence on the left and two large gray squarish pillars on the right.
Move slowly up to where you're past the nearest pillar, then look between them to see a stack of two large red storage containers. If you don't see an assassin's leg just to the left of that stack, slowly strafe left until you do. Shoot the leg with a dart to score an instant kill. Switch to the hornet gun and crouch-walk on past the fence to where you can see some explosive barrels in the distance between a large red storage container and a stack of green crates. Use altfire hornets to blow up those explosive barrels and the assassin that's standing next to them. (SRC: Watch for the second assassin to run over to the first one right after you kill her. Quickly kill the second one, and don't bother blowing up the barrels.)
Go down to where the explosive barrels you blew up were (or are), then go down the passage that's to the right of the big doors. Turn right to find some green crates that are stacked in such a way that you can use them to hop up onto the top of a large red storage container. Stay crouched as you hop up, and look over toward the upper walkway on the right as soon as you get onto the red storage container. You should see an assassin crouching in the area that's just past the right gray pillar. Shoot her in the head with the crossbow to finish her off.
Drop off the other side of the red storage container, then look to the left for a crate-clogged passage. Bash through the crates to find supplies and gain access to some stairs. As you bash the crates, you'll hear an assassin running onto the upper set of stairs. Get out the crossbow and go into zoom mode, then get to where you can just barely see the assassin's head when she turns it to the left. Shoot her in the head to kill her.
SRC: That assassin stays at the top of the second set of stairs, and there's no way to sneak-shoot her. Horneting her is also very difficult, so you'll probably want to use explosives (after quicksaving). Crouch-walk about halfway up the left side of the first set of stairs with the assault rifle out, then turn and fire an AR grenade at a spot just above the approximate midpoint of the second set of stairs. Or crouch-walk up the right side of the first set of stairs with your C4 satchels out, then toss one onto the floor just past the stairs. Stand up and run backwards, ready to hit the detonator as soon as the assassin runs into view.
Go up the stairs and along the left section of the walkway to reach the assassin you sniped from on top of a red storage container. Go down the stairs to the left to find a small area with first aid and HEV stations. Recharge on them, then go back up the stairs and straight forward until you reach a dark hallway with a small lift at its other end. Use the flashlight to help you find the button on the wall, then press it to get the lift to descend. After it stops, get off of it to start on section c3a2.
Section c3a2: ALIEN GRUNT AREA AND THE GLUON GUN
Go down a short hallway to find a large tunnel section with explosive barrels in it. When you approach the door past the barrels, it will open, and an alien grunt will be standing right behind it. What you should do is quicksave, then approach the door by moving slowly backwards. As soon as you hear it start to open, run forward and all the way to the lift. Wait there to see if a grunt follows you, and hit it with an AR grenade followed by a bullet stream to the face if one does.
Go back to the short hallway and fire some hornets over the nearby explosive barrels so they'll go toward the grunt-opened door. If there are any grunts near that door, the hornets should hit them. When a grunt teleports in nearby (this has already happened if a grunt followed you to the lift), turn and alfire-hornet the explosive barrels nearest him until they explode, then sneak-shoot him with the crossbow to finish him off if the explosion didn't.
Fire more hornets toward the grunt-opened doorway, moving to where you can partly see through it if necessary. There may be more grunts in the big room past the doorway, under the big orange sign. After you think you've gotten them all, quicksave and check. If you're right, find the ladder in the back right corner of the room and climb it to reach a walkway with a door that a scientist will open for you.
Turn left past that door to find some crossbow ammo on a green crate, then wait for the scientist to stop talking. Get him to follow you, then lead him to the closed retinal access door. After he opens it, you're free to whack him to death with the crowbar for not opening the room's outer door for you before the grunts were all killed. (After all, grunts can't climb ladders. What was he thinking?)
In the room past the retinal scan door, use the wall rechargers to get back up to full health and armor, then ride the small lift up by standing on it and using its button. Turn right in the corridor past the lift to find the door to a test firing chamber. Go inside and pick up the gluon gun from next to the scientist. When he says, "You don't look as if you have any trouble killing things," say, "No, I don't!" and blow him to bits with a quick gluon burst. Ha!
You can then use the buttons on the two control panels to open up the nearby firing chamber doors and blow away the headcrabs in the left chamber and the bullsquid in the right chamber. Fun and easy! When you're done, restock on ammo from the nearby shelf, then leave the room and go down to the other end of the corridor to find a button-operated lift that'll get you to section c3a2a.
Section c3a2a: REACTOR COOLANT SYSTEM COMPLEX
When the lift stops, get out the hornet gun and push up against the lift doors to get them to open. Fire some hornets at a spot just beneath the large lambda symbol on the big orange sign that's ahead and to the left. They should swerve down and hit a vort that you can't see. Move to the back of the lift and watch the passage to the right of the smaller "02 COOLANT SYSTEM" sign with the assault rifle out.
If the vort appears in that passage, quickly shoot it down. However, that's less likely than it going the other way and stopping next to an explosive crate that's near a hallway entrance to the left of you. If that happens, move close to the lift doorway and fire hornets to the left. They should hit the vort and cause it to move a short distance into the hallway. Peek out and blow up the explosive crate with altfire hornets, and that vort should die. (SRC: The vort won't move from its original position unless it sees you, so crouch-walk over to the railing and get to where you can sneak-shoot it with the pistol.)
There are two more vorts in the hallway that weren't hurt by the explosion. You could sneak-shoot them with hornets, but it would be much faster to shoot them with the shotgun. Approach their hallway entrance slowly until you see them, then quickly fire off a double-barrel blast and strafe left for cover. Strafe right when they're done firing and shoot them some more, perhaps using the explosive crate in the hallway to help blow one of them up. (SRC: Use an AR grenade to kill them both quickly.)
As soon as they're down, go to the back of their hallway, where it splits at a T-intersection with two large signs on the wall. Stop there and get out the hornet gun -- it's best to deal with the three sets of teleport-in aliens now. The first set has probably already teleported in, even if you didn't hear them. They're back in the area you just left. Go along the left edge of the hallway until you can see a vort on the walkway a ways over to the right (not far from the "02 COOLANT SYSTEM" sign).
Let it see you as you hit it with a few quick hornets, then back up a ways and use the assault rifle to shoot it in the head as soon as it comes into view. After it's down, move along the left side of the hall again until you can see the blue "01 COOLANT REACTOR" sign ahead and to the left. Fire hornets toward the sign, and they should swerve left and hit the alien grunt that's over there.
After it's dead, go back to the hallway intersection and turn right. Pass by a security guard with a bullet clip on a crate next to him, then go down some stairs and through a door to find a room with first aid and HEV rechargers, plus lots of ammo on a shelf. After filling up there, return to the hallway split and go down the other way. Don't open the door that's down that hallway -- just run to its end, and then return to the T-intersection. Doing all that should get the second pair of teleport-in aliens to appear, so repeat the above process of killing first the vort, then the grunt.
If the third and final teleport-in pair don't appear soon afterwards, go over to where the vorts appear, then go down the ramp past that to reach a hallway with a lot of red machinery along one side. Run back and forth along that hallway to hopefully get the final teleport-in aliens to appear. When they do, sneak-shoot them each from near the bottom of the ramps they're close to. If necessary, keep doing the two hallway-running routines described above until you get all three teleport-in alien pairs. (SRC: There's only one pair.)
After that, go get the security guard by the crates to follow you, then follow the blue "01 COOLANT SYSTEM" signs until you reach a spot with two dead scientists on the floor. Move down the hallway past them while facing toward them, since a vort will teleport in near them.
When it does, quickly move to where your security guard is directly between you and it. After the guard gets zapped, move to where you can shoot the vort with altfire hornets. Your guard should help you take it down if he survived the zap. If he's still alive afterwards, whack him for his ammo. (If this routine doesn't work for you for some reason, drop a C4 satchel bomb on the floor near the dead scientists, then back up down the hallway and hit the detonator's button as soon as the vort appears.)
Move up to the door at the other end of the hall to get it to open, then stop and fire some hornets over toward the left side of the room beyond. There are three alien grunts over on the room's left side, one of which is up on a higher walkway. You'll want to hornet them all to death from the doorway before moving into the room. (SRC: When opening the door, be extra careful that none of the grunts see you.)
Climb the ladder that leads to the room's upper walkway, then go along it to reach a door. Past it, go up some stairs and turn right to find the pump room. Use hornets to kill the nearby headcrab, then move forward to where you can see and hornet another headcrab that's on the room's lower floor, to the right of the big blue pump machine. Move forward to where the walkway splits, then quickly retreat back to the corner by the stairs.
Wait for two vorts to teleport in, then move to where you can use hornets to sneak-shoot the one that's on the upper walkway over to the right. (SRC: It's much easier to wait at the walkway split with the shotgun out.) After it's down, crouch-walk along the walkway until you get to a spot where you can use the crossbow to sneak-shoot the vort that's on the other side of the big blue pump machine.
Move along the side walkway and examine the pump machine with the flashlight on until you see its little red lever. After quicksaving, drop off the walkway at the spot nearest the red lever, then use it and run for the ladder that'll get you back onto the walkway. Two more vorts will teleport in, but if you're fast enough, you can leave the area without getting zapped.
Make your way back to the hallway with all the red machines, then follow the "02 COOLANT SYSTEM" signs until you reach a spot where an explosion blocks the hall with rubble. Crouch-walk past the first big piece of rubble on its left side, then turn right and jump onto the piece of rubble on the floor, then move to its other end and turn left. You can then easily make it to the door that's just ahead.
The room beyond this door is similar to the room beyond the hallway door in the previous area, except that the alien grunts in this room aren't all nicely clustered off to one side. If you stand in the doorway this time, you'll be seen and horneted. What you want to do is have the gluon gun out when you first open the door so you can use it to quickly kill the grunt that's directly across the room.
SRC: If you're crouched when you open the door, that grunt won't be able to see you. Altfire-hornet the explosive crate that's on his side of the room, then fire hornets at him over the large white hanging thing. If your hornets insist on going up, sneak forward far enough to altfire-hornet the barnacle that's hanging over the upper walkway.
After he's dead, you can switch to the hornet gun and sneakily hornet the grunt that's over on the right side of the room. To help keep him from seeing you, back up a little right after opening the door. Those are the only two grunts that start out in that room, so go on in after they're dead and use altfire hornets to kill the three barnacles (one of which is hanging over the upper walkway).
Check near a dead scientist for health packs, then set a tripmine to trip up the third grunt when it teleports in. Find the big "COOLANT TANK 02" sign on the wall, then notice that the wall is divided into segments by vertical lines. After quicksaving, place your tripmine in the center of the second wall segment to the right of the coolant tank sign.
Climb the ladder and move slowly and cautiously along the walkway until the grunt teleports in and falls through the walkway just ahead of you. If you put your tripmine in the right spot, the grunt will fall right into it and get blown up. If not, quickrestore and try again. After you get it right, jump over the walkway break and go along until you reach a door.
Just past the door, use the wheel on the right wall to turn off the steam, then crouch-walk through the rubble and go up the stairs. Turn left at the top of the stairs and quickly hornet-shoot the two headcrabs you see on the walkway ahead. Use the flashlight to help you see the third headcrab on the floor near the big orange pump machine, then hornetize it and the three barnacles on the ceiling before dropping down to the floor.
Get the armor batteries near the dead scientist if you need them, then use the pump machine's little red lever to get it going. Use the ladder to get back onto the walkway, then go back the way you came. Revisit the downstairs room with the scientist and the supplies to see if there's anything you need there now, then go the other way from the hall T-intersection and approach the door that I told you to go by without opening before.
Do a quicksave, then open the door and run through it. In the middle of the room beyond is a large tank with a little water in its bottom. If you run and drop into the water fast enough, the alien grunts in the room won't have time to hornet you. Find the maintenance access tunnel and start swimming down it. When you enter a small room where you can surface for air, section c3a2b will load.
Section c3a2b: ASCENDING THE CORE
Swim through the short tunnel that leads from that room to the base of the reactor core. Look up and to the left to see the head of a vortigaunt that's standing near a ladder on the lowest ledge that circles the core. There's no need to shoot him, but remember where he is. Look around underwater for two small flow control valve wheels on the walls.
Use either one of those wheels, then wait for the water level to stop rising before you use the other wheel. After the water level stops rising again, float on the surface in a spot where the vort you spotted can't zap you, and wait for it to be zapped by one of the core's electrical discharges. After that happens, climb up the nearby ladder to a spot near its top, then look up and locate the stray electrical bolt that's moving slowly around just above you.
Right after it goes by you, climb onto the ledge, turn left, and run for the next ladder. Stop and quicksave once you're near its top, since it's going to get harder. When you climb up onto the second circular ledge, you'll want to turn right and run for the nearest ladder, so watch the multiple moving electric bolts to make sure that you don't get zapped on the way. If you do, quickrestore and try again until you make it unharmed, then quicksave again.
On the third and final circular ledge, you'll want to turn right past the ladder, jump a gap in the walkway, and then run for the alcove with the door. You're safe in the alcove as long as you don't let the electrical beam that hits the center of the door touch you. Wait until just after it goes off, then go through the door and run to the right. Go down the corridor until section c3a2c loads.
Section c3a2c: ALIEN BATTLE HALLWAY
Go through the "SUPPLY D-301" door and check the shelf for stuff you need, then enter the nearby malfunctioning elevator and elevate yourself by climbing the ladder in the back. At the top of the ladder, turn around and jump to the broken elevator door to reach level B. Go through the "SUPPLY B-301" door and check its shelf for goodies.
Leave the supply room and go down the corridor until you reach a door on the right that leads to a room with a security guard. Go past the door and turn right, then walk up to the crate you see ahead. Immediately back up until you're by the security room door, and have the shotgun ready to double-barrel the vort that teleports in a bit to the left.
Hopefully, neither of the two grunts who teleported into the hallway past the crate you approached have seen you. If that's the case, you can carefully sneak-shoot them both to death with hornets. (Note that one of them likes to hide in the second doorway on the left in their hall.) If they see you, you can run back to the fallen door in the elevator shaft and sneak-shoot them from on it. After they're both dead, find the large red wheel on the wall and use it to cause the steam vents farther down the hall to spray painfully hot steam. (SRC: The steam is already going, so don't use the wheel yet.)
Go toward the steam, but don't enter it. As you approach it, aliens will start teleporting in at the other end of it. As soon as they do, run into the nearby room and go through the door in its back right corner. Hopefully, this will keep you from getting hit by any hornets. Wait a few seconds, then return to the doorway that leads out to the hall. Fire some hornets toward the steam to see if you can hit anything. Strafe into the hall just long enough for any surviving aliens to see you, then run for cover again as they enter the steam and die.
If all you got were vortigaunts, you could toss a hand grenade toward the back wall past the steam to see if that'll get the teleport-in alien grunt to appear. If you don't do that, it'll probably never appear, and you won't have to worry about it. Go shut the steam off by using the same wheel again. There are two more grunts around the corner past the steam vents, so quicksave and then try to sneak-shoot them with hornets.
If they keep running into view and attacking you when you do that, you may want to quickrestore and go get the security guy to help you. (Or sneak-shoot them with heavier weapons, like the crossbow.) After they're down, go to the end of their hallway to find a ladder that leads down to a small optional part of section c3a2f. To make sure you don't take a painful fall, crouch-hop onto the railing and run onto the ladder from there.
Section c3a2f: SIDE AREA WITH SUPPLIES
In the room past the bottom of the ladder, look on the floor next to the big reactor core diagram to see that someone (presumably the nearby dead scientist) wrote the numbers 2, 4, and 7 in blood. Remember those, since they'll be significant soon. For now, use the stacked crates to hop over the fence they're next to and land on the middle walkway of the dark and wrecky room beyond.
Carefully crouch-walk under the fallen beam to get to a health pack and some gauss gun ammo. Crouch-walk back under the beam, then use the ladder that's on the left part of the fence to get back over it. That's all you can do here, so go back up the tall ladder that'll return you to section c3a2c.
Section c3a2c (again): ASCENDING THE CORE, PART 2
Go through the "CORE LEVEL B" door that's down a nearby side hall, then walk up next to the teleporter orb that's closest to the core fence. Look to the nearest orb that's past the fence, and watch for a rotating platform to move under it. When one does, enter the portal you're next to in order to end up on the moving platform.
You'll be rotating around ports 1 thru 3 of the core. Port 2 is the one that gets you up to the next level, but first jump into port 1 to get teleported to a headcrabby area. Stand where you appear and hornet-kill the headcrab that you see ahead in the grate-floored room. After it's dead, another will drop down near the ladder in that room, so kill it and any that drop down after it.
Next, kill all of the headcrabs in the two dark side niches along the right wall, using the flashlight to help you see them. Each niche has a total of three headcrabs, which will drop down one at a time. After they're all dead, go to the edge of the grated-floor room and look to the left to spot a headcrab near the wall. Kill it with hornets, then wait for more to fall. (If none do, look up to see if any got stuck up near the ceiling.) Don't neglect to also kill the headcrab that you can see to the left of the portal on the platform at the other end of the room. (SRC: The only headcrab in the area is the one that's near the portal.)
After they're all dead, use altfire hornets to shoot all of the floor gratings to see which ones will break. Or skip that and just walk along the floor beam that goes all the way across the room to a spot near the ladder on the other side. Jump to the ladder, then climb it to the portal platform. Get the hand grenades from a crate near the portal, then go through it to return to the starting teleporter area.
After you get back onto a rotating platform, go through port 3 to get to a secret supply room with stuff on the shelves. Get what you need, then use the exit portal to return to the starting teleporter area. This time, you'll want to go through port 2. However, don't just jump from the rotating platform into the port. You need to jump to the port 2 ledge, which can be tricky to do without being teleported. Try jumping to the ledge when your rotating platform isn't in front of port 2 yet, but is just coming around to it.
Quicksave, then turn and look up. You see that portal that's almost directly up above you? That's where port 2 will take you, so wait until you see a rotating platform under that portal, then quickly back up into port 2. Immediately start crouching, since the rotating platform will go under a pipe between ports 6 and 4. Wait until you can jump into port 5, which will take you to a room with supplies on a shelf and three scientists.
Go through the room's door and down a hallway to reach another room with supplies on shelves, plus a portal that'll take you back to the starting teleporter area. Go through port 2 to get to the next level again, then jump over to port 4's ledge and quicksave (just like you did with port 2). Look up and right to see the portal that port 4 takes you to, and back into it when there's a moving platform to land on.
Again, crouch whenever your platform is about to move under a pipe. Jump into port 8 to be taken to a room in section c3a2b with an HEV station and some gauss gun ammo. As soon as you materialize there, get out the assault rifle and run for the opposite wall (the one with a big window in it). Crouch down next to the wall so the vort that teleports in on the wall's other side can't zap you, then turn to face the room's door. The second teleport vort will appear near it, so shoot it down quickly.
Wait until you hear the first vort being killed by zappy electrical discharges, then go for the HEV station and the gauss ammo. Use the exit portal to get back to the starting teleporter area. Now it's time to get serious about getting past this area. Go through ports 2, 4, and 7 (like the scientist wrote on the floor in blood) to get to the fancy core area in section c3a2f.
Section c3a2f (again): LEVEL C REACTOR CORE
Stay on the ledge you start on and study the complicated reactor mechanism ahead of you. There are two sets of rotating platforms, plus a large circular ring between the platform sets that goes slowly up and down. That ring is going to be your primary means of transportation around this place, but notice that its highest position is up against large ceiling beams in several spots. You don't want to get crushed against those while on the ring.
What you want to do is quicksave, then take a running jump from your ledge to the circular ring when it's on its way down to its lowest position. As soon as you land on it, turn left and run along it until you find a ledge on your left that has a button marked "01" on its back wall. Wait until the ring rises up to where it's about even with the ledge, then take a running jump toward it (using a moving platform between you and the ledge to help you get there).
Press the "01" button, then quicksave and repeat the process of jumping to the ring when it's on its way down. As before, turn left and run along the ring until you're near another button ledge, this one with an "02" label. Jump to that ledge when you can, then press its button. The two "doors" that lead into the central core are now open enough for you to get through them.
After quicksaving, jump back to the ring and then to one of the moving platforms that are between the ring and the central core. When your platform is next to one of the open core "doors," move forward onto the door's ledge, then crouch-jump through the door and into the portal to be taken back to section c3a2c.
Section c3a2c (yet again): DONE WITH THE CORE
You're now past all the horrid core areas, so save your game in celebration and do not enter the exit portal nearby. It'll take you all the way back to the starting teleporter area, and you don't want to go there. Instead, go through a couple of doors to get to section c3a2d.
Section c3a2d: TELEPORTING TO THE ALIEN DIMENSION
Past the second door, go up to where the red wheel on the overhead pipe is and use it. (You may have to get under it and jump right before pressing the "Use item" key.) Wait for the steam to kill three headcrabs at the other end of the hallway, then use the wheel to turn it off so you can move into a dark area past the headcrabs to find an armor battery. (SRC: Two armor batteries.)
Near that dark area is a side alcove with a ladder in it. Climb it to the top, then go down the corridor to find a closed door that a scientist will open for you. (I've heard that this scientist is supposedly Dr. Isaac Kleiner in Half-Life 2, but I see no particular reason to assume that.) Go through the open door and check all around for tons of supplies while the scientist talks to you.
After he opens the long jump module case, move into it to pick up the module. To use it, run forward and crouch, then jump right away. When the scientist opens the door to the next area, get him and the security guy to follow you through the noisy scanner. Use the first aid and HEV stations if you need to, then enter the big teleporter chamber.
Leave the scientist and guard near the chamber's door, then save your game. In a short time, alien controllers are going to be teleporting in. You don't want them attacking your gate-opening scientist, even though he has some protective glass around him. That glass won't last for long, and if he dies before you can teleport out, it's game-over time.
You don't have to frantically kill controllers as fast as they appear in order to save the scientist. All you have to do is distract them so they'll attack you instead of him. A good place to do this from is on top of the high-up ledge you can get to by climbing up a red ladder on the wall. Run around the chamber until you find it. The bad part of this way is that you have little room to dodge without falling off the ledge, and will therefore take a lot of damage. Add to that the damage of dropping off the ledge when you need to hurry and get into position for the teleport, and this is one painful strategy.
Before you try the ledge method, you should try standing on the floor on the opposite side of the chamber from the gate-opening scientist, near the narrow ledge that leads to the teleporter core. You won't be quite as visible to the alien controllers there, but most of them should still come after you. You might have a problem with the controllers that teleport in near the above-mentioned high-up ledge, so watch for them and quickly shoot them with something to get their attention as soon as they appear. (NOTE: Don't use the gauss or gluon guns at all, since you'll need all of your ammo for them in Gonarch's lair.)
When the gate-opening scientist says to get into position, do a quicksave and then run over to the spot on the floor that's on the opposite side of the chamber as the scientist (if you're not already there). Keep distracting alien controllers and dodging their fire until the scientist says you must go through now. Immediately run along the narrow ledge that leads up to the portal and jump into it. If you're fast enough, you'll be teleported to the "Xen" chapter even if the scientist gets killed.
SRC: The alien controllers will come after you with a vengeance, making it impossible to survive unless you kill them as quickly as you can. I found that using the assault rifle to shoot down two controllers in each wave and blast the third one with an AR grenade worked pretty well. Quicksave after every wave in which you don't take too much of a pounding, and watch for the teleporter to be ready. (Note that you probably won't be able to hear the scientist say it's ready, so once it starts to form, try jumping into it after every quicksave you make.) As an alternative, keep running around the chamber and doing long jumps to avoid controller fire while waiting for the portal to be ready. Since the controllers are fanatical about attacking you, the gate-opening scientist should be safe. If it works, you'll end up much healthier and with more ammo.
Section c4a1: HUGE FLOATING ISLAND
No matter how damaged you are, save your game in a regular slot as soon as you make it here. Do a couple of quicksaves too for good measure. You just made it past the first of the three hardest parts of the game. (If you end up in really bad shape, save here anyway, then restore an earlier save and try the teleporter chamber again to see if you can do better next time.)
The first thing you need to do here in Xen is long-jump over to the floating rock that has a dead HEV guy on it with a health pack and armor battery next to him. To make the jump, run forward while facing the HEV guy's rock, then crouch and jump right before you reach the edge of your rock. Since you've made several saves, you can easily restore one and try again if you don't make it. (SRC: Hide behind the ledge's rocky spire as soon as you land on it, since the vort that's mentioned below can zap you if you don't.)
After you get the health and armor, use the hornet gun to kill the vortigaunt that teleports in on the next floating rock in the series. Long-jump over to his rock, then wait with the shotgun out for another vort to teleport in. Quickly blow him away, then dispose of the houndeye that 'ported in behind the small rocky spire with the crowbar or hornet gun.
Now comes the long, arduous task of getting down to the top surface of the main rock "island." If you try to long-jump straight there, you'll fall more than far enough to die from the impact, even in this dimension's lower gravity. Study all the rocky platforms that are moving around the island's huge spires at various heights until you find the highest-up one. Long-jump to it when it comes close enough to your rock for you to do so.
Look down to find the next-highest platform, then wait for it to come to where you can drop down onto it. (Note that it might help a bit to crouch before you land.) Keep dropping or long-jumping onto the next-highest nearby platform until you reach the lowest one, from which you can drop to the surface of the island without taking any damage. (And yes, you should quicksave after every successful dropping-down, just in case you mess up on the next one.)
Move carefully around the border of the island's top surface to see that there are four large spiky protrusions sticking out a ways below you. There's also a small moving rock platform that goes around the island's circumference. You could move around the island border and watch the platform until it gets close enough for you to drop safely onto, but that's not the best way.
After quicksaving, crouch-drop very carefully onto any of the four spiky protrusions, then stay crouched and see if any nearby hanging purple crystals can zap you. If so, quickrestore and try dropping onto a different spike. Once you find one where the nearest purple crystal can't zap you, use the hornet gun to quickly kill any nearby houndeyes, then use altfire hornets to destroy every purple crystal within sight, starting with the closest one.
After that's all done, jump-crouch onto the ledge that runs around the lower part of the island. Make your way slowly along the ledge, using hornets to kill houndeyes and destroy purple crystals as you go, until you find the big healing pool. Stand in it until your health is back to 100, then examine the rocky wall near it carefully with the flashlight on until you find a small space you can crouch-walk through to reach a sort of hidden alcove.
Jump-crouch into the large hole in the alcove wall, then bash through the vines to reach a big room with an alien teleporter in it. To activate that teleporter, you must first go around the room and find all three of the weird mushroom-like things with metal claws on top of them. Use each of those three shrooms to open its claws. (Note that you'll have to jump to one of the shrooms, since it's on top of a large rock.)
After they're all open, find the vines that are imprisoning three little golden flyer thingies. Bash the vines to release the flyers, then wait and watch as they settle into the open-top shrooms. After all three of them are in place, the exit teleporter will be open in the center of the cave. Big rock "fangs" will start coming out of the cave's floor and ceiling, so quickly run into the teleporter beam to get to the "Gonarch's Lair" chapter.
Section c4a2: GONARCH COMBAT, STAGE 1
As soon as the area around you fades in, run for the nearby armor batteries and ammo canister, then use the hornet gun to kill the two headcrabs that are coming for you. Look a bit to the left of and beyond those headcrabs to see a cluster of three spiky plants next to a large rock wall. (Both the plants and the wall are near the area's border.)
Run for those plants, then go between them and the rock wall. You can hide from Gonarch (short for Gonad Monarch, no doubt) behind the rock wall, and you can go along the ledge behind it to get to a spot where you can long-jump to and from a healing pool. To damage Gonarch, fire hornets at it through the gap between the rock wall and the three-plant cluster.
Gonarch's vulnerable spot is the huge glorpy sac that's hanging down under its main body. Fire hornets while aiming a bit below that sac, and they should swerve up and hit it. They should also swerve to hit any little white baby headcrabs that Gonarch births. If Gonarch ever fires off a glob of acid at you, run quickly along the ledge behind the rock to make sure it doesn't hit you. (The acid attack shouldn't ever happen if you stand so that you can only halfway see Gonarch. SRC: That's difficult to do since Gonarch runs around a lot more.)
Gonarch will mostly stand still as you attack it with hornets, though it will run around briefly every once in a while. When it's finally damaged enough to get scared, it'll run off and crash through some vines that are blocking a cave tunnel entrance. After you make sure you've killed all the baby headcrabs in the area, come out from your hiding spot and enter the cave tunnel.
Move along it with the flashlight on to find an armor battery and ammo canister near a dead HEV guy. (Say, how did all these HEV guys get here ahead of you, anyway?) Be sure to save your game at this point, since the second of the three hardest parts of the game is coming up. Move on past the HEV guy to reach the spot where section c4a2a loads.
Section c4a2a: GONARCH COMBAT, STAGE 2
As soon as this section finishes loading, run forward to avoid getting crushed by a rockfall, then get out the gluon gun and start blasting Gonarch's sac with a continuous stream of fire. Discontinue fire if Gonarch moves left or right, since it's hard to keep from missing then, and resume fire again as soon as you can be sure of your aim. When Gonarch spits acid at you, running forward is usually the easiest way to avoid it.
You should start out with a full load of gluon ammo, which may be enough to get Gonarch to quit attacking you and crash through the vines that lead to the next area. If not, quickly switch to the RPG or assault rifle and start blasting Gonarch's sac with rockets or AR grenades. If Gonarch manages to hit you even once with its acid or its spiky legs, you'll probably want to quickrestore and try again. You also might want to try using three or four RPG rockets to start with, then switching to the gluon gun.
An alternative to using the gluon gun is to use fully powered altfire blasts from the gauss gun. Three such blasts should be enough to get Gonarch to flee the scene. Stay way back near the cave-in and wait for Gonarch to stop at the other end of the area, then power up an altfire blast and hit Gonarch with it. If that doesn't knock you into the corner next to the rubble, quickly move into it and start charging up another altfire blast. By the time it's fully powered, Gonarch should have run into view. Blast it again, then quickly switch to the hornet gun to shoot down any baby headcrabs it may have released. Switch back to the gauss gun and start powering up another altfire blast, which should be ready by the time Gonarch appears again. That'll be the third blast, so finish off any last baby headcrabs, then go make sure Gonarch moved on to the next area. (Note that it can hit you with acid while you're in the rubble corner, but it won't get the chance if you blast it fast enough each time it comes after you.)
SRC: Gonarch can take a lot more damage than in the original game, so really lay it on with the rockets, AR grenades, and whatever else after exhausting the gluon gun's ammo supply. (Don't even bother trying the gauss gun altfire strategy.) Your best option is to run straight for the trapezoid-shaped hole mentioned two paragraphs down as soon as you enter the area. Get to the healing pool, then stand in its "doorway" and shoot up at Gonarch from there with the hornet gun. You could use rockets and the gluon gun to speed things up, but if you're patient enough, you can get Gonarch to run off to the next area using only hornets. (Note that it can be really useful to have a full load of gluon ammo in the first part of the "Interloper" chapter, so try to avoid using any of it here.)
NOTE: I don't recommend the above SRC note strategy for any non-Source version of the game. That's because Gonarch may glitch and become invincible to all weapons if you fire up at it from down below. Feel free to try it if you like, since it'll sometimes work, but be sure to keep a save that you can fall back on if it doesn't work. (It seems to glitch less often if you drop down using the trapezoid-shaped hole rather than dropping directly onto one of the pit area's ledges.)
Before you follow Gonarch to the next area, look for the large trapezoid-shaped hole in the ground in the back corner of this area. Drop into the hole, then walk along until you come to a small stick-out rock. Turn around and crouch-walk backward onto the stick-out rock with the flashlight on, ready to shoot the headcrab that magically appears in front of you with some fast altfire hornets. Stand up and turn around, then quickly jump to the stick-out rock on the left before more headcrabs can spawn. (Note that you could drop down to that rock directly without using the trapezoid-shaped hole, but that's a bit more error-prone.)
The small room past that stick-out rock has a healing pool in it. Stand in the pool until your health is 100, then return to the stick-out rock and jump from it over to the only one you haven't been on yet. Quickly kill the headcrab in the room beyond with hornets, then collect the ammo canister and armor batteries that are near yet another dead HEV guy.
Slowly make your way around to the back of the whoosh-thing on the ground, then quicksave. Run onto the whoosh-thing and jump, trying to get through the large hole and land safely on the ground outside without taking any damage. If you mess up, quickrestore and try again until you get it right. Once you're back up there, you can follow Gonarch into the cave it ran into earlier.
When you come to the cave shaft, jump across to the narrow ledge that has the light crystal on it. Turn around and jump toward the light crystal you see in the wall below and across the shaft from you, then crouch as you fall. You should drop into section c4a2b without taking any damage.
Section c4a2b: GONARCH COMBAT, STAGE 3
After you reach the floor, turn around to see Gonarch jump into a pit at the other end of a short cave tunnel. The floor of that tunnel is very slippery, and you'll have to be careful on it to keep from falling off the edge and dropping down to where Gonarch is. You could skip having to kill Gonarch by dropping down there and using explosives to break the patch of flooring that's next to the spiky plant cluster. (It's the patch that's destroyed when Gonarch blows up.) However, you'll be under constant attack by Gonarch's acid and baby headcrabs, so this isn't the best strategy. (SRC: It takes a lot fewer explosives to open up the hole than in the original game, so you might want to consider doing it.)
Move into the tunnel slowly, and you'll soon start sliding toward the drop-off. If you were moving slowly, you'll only slide slowly, so let it happen until you're about halfway down the tunnel, then lean on the "Move backward" key until you stop moving. You should then be unable to move in any direction unless you jump first or really lean on a movement key, but don't do that yet. Get out the hornet gun and start firing hornets at a spot over the drop-off. They should swerve down and hit Gonarch.
SRC: Once you start sliding down the tunnel, it'll be impossible to stop yourself after you get past the first patch of slipperiness (unless you're hugging either side of the tunnel). After quicksaving, carefully crouch-walk forward until you start sliding forward, and note where that happened. Quickrestore and move as far forward as you can without starting to slide, then quicksave again. You can then jump up and down while firing hornets toward the two big alien plant clusters you can see on the ceiling above Gonarch. A lot of hornets will go astray, but some of them will swerve down and hit Gonarch.
If you don't hear any "crunch" sounds that signify the hornets are doing damage, try firing them at various spots, including high-up ones. Also, try changing your position a bit and jumping up and down while firing hornets. (Just be sure not to slide too close to the drop-off, or Gonarch will be able to throw acid at you.) It takes awhile, but you can eventually get enough good "crunch" hits to make Gonarch change position, after which it should be easy to score hits without having to jump or move around at all.
If you can't ever get any "crunch" hits at first, or if getting Gonarch to change position is taking too long, toss some hand grenades and/or C4 satchel bombs to damage Gonarch. Note that with the grenades, it can be kind of hard to make sure they hurt Gonarch, since they can bounce off to the side or fall through the vines that Gonarch is standing on. With satchels, it's easier to hurt Gonarch, since you can hit the detonation button as soon as the satchel falls out of sight. You'll have to jump right before throwing one, then lean on the "Move backward" key to make sure you don't slide forward.
Hit Gonarch with explosives until you hear it change position, then try the hornet gun again, remembering to fire hornets at different spots (and jump and change position) if you don't start getting the "crunch" sounds right away. Hopefully, you won't have to use any more explosives, and can keep horneting Gonarch until it blows up.
After Gonarch is dead, turn the flashlight on and jump up so you can start moving slowly forward. (SRC: Fire a bunch more hornets down the tunnel before sliding down it to hopefully kill off all the baby headcrabs in the pit.) Aim yourself toward the left side of the drop-off. As soon as you go over the edge, lean on the "Move backward" key to ensure that you land on a tiny ledge a ways above the floor below. Use the flashlight to help you see and hornet-shoot all of the baby headcrabs on the floor. They won't all be running around, so take the time to scan the whole floor carefully before you crouch-drop down to it. (SRC: You can't land on a ledge, so crouch down and lean on the "Move backward" key as you go over the edge, then run for the dark corner near the armor batteries. Hornet-shoot baby headcrabs from there if there are any left.)
No matter how careful you were, there will still probably be some baby headcrabs left, so be sure to hornet-kill all of them before you grab the four armor batteries that are clustered together in a dark corner. Get the ammo canister that's fairly near the batteries, then go over to the large hole in the floor that Gonarch made when it blew up.
If your health is under 100, carefully crouch-drop onto the edge of the hole's side area that has a health pool in it. After you've healed up, save your game in a regular slot and a quicksave slot, then drop to the bottom of the hole to get teleported to the "Interloper" chapter.
Section c4a1a: BIG ISLAND WITH ELEVATOR SPIRES
The regular way to get past this area involves going through the cave that starts on the other side of the island. Even though the cave has some supplies, including gluon gun ammo in a canister, it's definitely not the best way to go. You'll be giving the aliens more time to teleport in vorts and controllers, and you'll not be able to avoid getting badly vort-zapped as you ride up the "elevator spire." Due to this, I will only describe the two shortcut methods that I've discovered. (Note that shortcut #2 is a lot quicker, but can be harder to do. SRC: Shortcut #1 may not work, leaving #2 as your only option.)
SHORTCUT #1: RUN TO ELEVATOR SPIRE
When the scene starts to fade in, turn left a bit so you can see the nearby parts of the large island you're next to. Watch for two huge rocky spires to rise up out of the ground, and note exactly where the hole is that the second one rises up out of. Restore your game from the end of "Gonarch's Lair," then drop into the teleporter again. Turn and run for the second spire's hole as soon as you can see where you're going.
When you make it to the edge of the hole, look down into it to see the rocky spire's top. When it starts moving up, drop onto it and ride it all the way up. Look around for a floating rock platform nearby that you can jump to, then quicksave and start shooting down all the nearby alien controllers. Use the gluon gun until you run out of ammo for it, then switch to the .357 and/or assault rifle. (The shotgun is good for controllers that fly by really close.)
After all the nearby controllers are dead, quicksave again, then look for the next-lowest moving platform in the series. Yes, this is just like the moving platform drop-a-thon you went through in the "Xen" chapter, except this time you're not trying to get onto the island's surface. Instead, you're going for a stationary rock platform with an ammo canister on it that's a ways above the surface. Keep watching for (and shooting down) alien controllers as you make your way down to that rock. Once you're on it, you'll be in range of all the vorts on the island's surface, so stay crouched and move around when necessary to avoid getting zapped.
Watch for an alien flyer to appear and fly right by your rock, close enough that you can run onto it without having to jump. Once you're on it, get out the assault rifle and crouch near the flyer's center, quickly AR-grenading any vorts that are in a position to zap you as you ride along. When you get close to the large floating rock with an alien teleporter gadget on it, quicksave before long-jumping to the rock in case you miss it. Once you make it, enter the teleporter to get to section c4a1b.
SHORTCUT #2: LONG JUMP TO FLYER
When the scene starts to fade in, turn left just a little bit, then run forward so that you land near the right edge of the island below. Run along it to get up onto one end of a rocky hill, then get out the crossbow or .357 and snipe the vortigaunt that's standing around near the other end of the hill. Run over there, get out the gluon gun, and quicksave.
Crouch down on the lower part of the hilltop so any vorts on the ground nearby can't see you. (One may run up after you, so be ready to blast it quickly if it does. SRC: A couple of aggressive alien controllers will swarm you, too.) Locate the stationary floating rock that's a ways beyond your hilltop position. You can't long-jump to that rock, but you need to keep a close watch for an alien flyer to appear near it and fly right past it.
Before one does, use the gluon gun to blow away alien controllers, switching to the .357 (SRC: assault rifle) after you run out of gluon ammo. As soon as a flyer appears near the rock, quicksave again and try long-jumping onto the flyer. That's a very hard jump to make, so you may have to quickrestore and retry many times, especially if you're not good at doing long jumps. I found it best to long-jump off of the highest point of the hilltop while running toward the flyer. Once you make it, crouch-walk to the approximate center of the flyer.
Get out the assault rifle and start using AR grenades to quickly blow up any vorts on the ground below that can zap you. As for any remaining alien controllers, you can try to shoot them down, but it would probably be best to ignore them and focus on the vorts, since they can hurt you a lot faster. When you get close to the large floating rock with an alien teleporter gadget on it, quicksave before long-jumping to the rock in case you miss it. Once on it, enter the teleporter to get to section c4a1b.
Section c4a1b: SMALL VORT CAVE, GARGANTUA LAIR, AND SEVERAL TENTACLES
No matter how damaged you are, do the routine of making a regular save and two quicksaves, since you've just passed the last of the three really hard parts of the game. It's all downhill from here! (As long as you keep using my best strategies for everything, that is.)
Go through all of your weapons and make sure they're all reloaded, then get the armor batteries that are next to a dead HEV guy and behind the teleporter structure you appeared on. Leave the cave and turn left, then crouch-walk over next to a large broken-off rocky spire piece. Move around slowly until you can see an alien grunt on top of a hill in the distance.
Edge over to where you can only see the lower part of the grunt, then fire hornets toward it until it falls over dead. Crouch-walk under the broken spire piece, then move over to the base on the left that it broke off of. Strafe right until you can see the other grunt-on-a-hill a ways ahead, then move to where you can only see part of it before sneak-shooting it with hornets. (If either of those grunts see you, they'll signal for a flyer to drop off more grunts, and you don't want that happening.)
As you move carefully forward between spiky plants, look around the two up-n-down machines ahead to see if you can spot any vort workers near them. If so, quickly hornet-shoot them before you approach the machines, using the spiky alien plants for cover. After the outdoor vorts are dead, look to the right of the rightmost up-n-down machine for a cave entrance.
Quickly hornet-shoot the vort that's inside the cave, then look for another vort hiding just to the right of the cave entrance. After killing them both, enter the cave and go left and around to where you can kill another vort near the cave's back exit. Get the ammo canister that's near the back exit, then look outside to see a rotating rock.
You could jump to the rock and then over to the healing pool (or long-jump straight to the pool), but it would be a bit safer to go back out the cave's entrance and turn right, get on the nearest up-n-down machine's raised ground, and then jump onto the hill and run past it to reach the health pool. After getting your health back up to 100, jump back onto the hill and return to the cave entrance.
Reenter the cave and turn right to see the entrance to a room with a lot of supplies in it. There's a vort hiding in the room to the left, so carefully move to where you can sneak-shoot it with hornets before you go for the supplies. There are four health packs, three armor batteries, and two ammo canisters! Unfortunately, entering the room causes three alien controllers to appear outside the cave, and you'll have to deal with them next. Note that you should do so before picking up the ammo canisters. (SRC: No controllers will appear.)
Leave the supply room and slowly crouch-walk your way to the cave's entrance. When you can see a controller hovering in the distance between two rocky spires, take it down with a bunch of fast altfire hornets. Next, go to the cave's back exit and crouch-walk around while looking out of it until you see another hovering controller. If you stay inside the cave, it shouldn't move around or fire orbs at you, so you can use altfire hornets to kill it, too. If it does move and start firing orbs, use regular-fire hornets and dodge the orbs.
The best way to get the third and last controller is to get out the crossbow and slowly move backwards out of the cave's back exit while looking up and to the right. If you're careful, you'll be able to see the controller's big, fat head before it sees you. Quickly fire two darts into that head to kill the controller before it can register your presence and start moving around.
The whole outdoor area is now completely secured unless you count the unkillable tentacle in one corner. Get the cave supply room's ammo canisters if you haven't already, then find the big cave entrance that's a ways to the left of the two up-n-down machines. (It's a bit to the right of the tentacle.) At the back of the cave's entry area, turn left and hop up some rocks to find a tunnel that leads to a big healing water cave. Watch out for the opportunistic barnacles!
Return to the cave entry area and look to the left of the rock-blocked passage to find a narrow ridge that leads up to a hidden supply area. To get up the ridge, jump onto its lowest part, then keep jumping your way up as far as you can. If that doesn't get you to the supply area, try crouch-walking in spots where jumping doesn't work (like at the top of the ridge).
After you loot the secret supply area, go back down the ridge to the floor, then look down the rock-blocked passage. Use some altfire hornets to break the vines you can see at the other end of the passage. That'll get the gargantua down there to start crashing his way toward you, so quickly run back outside and up onto the nearby large hill. (You could instead run for the hill with the vort cave in it and stand near the fallen spire, but that doesn't work as well in my experience.)
Wait and watch for the gargantua to make it outside and see you, then move around on your hill to get him to run over to the area with all the spiky-tipped plants clustered together. Those plants can hurt him, so try to find a spot on your hill where you can stand so that the gargantua will remain near the plants and keep getting hit. You might want to shoot the plants nearest him with altfire hornets to make sure they keep swinging. Dodge the gargantua's sonic stomp-blasts when you have to, and wait for the plants to destroy him for you.
SRC: There's a glitch (yes, another one) that'll cause the gargantua to be unable to bash his way past the two large rocks near the cave entrance. He'll just pace around in the area next to the rocks endlessly. You won't be able to get past him or use the plants to destroy him. Your only option is to destroy him with grenades and rockets (or the gluon gun). If you want to use some tripmines and/or C4 satchels, too, get them set up before you break the last of the vines in the passageway.
SRC: On rare occasions, the two rocks near the cave entrance will self-destruct, or you'll be able to destroy them. This seems to be more likely to happen if you move a ways down the tunnel as you're destroying its vines. However, it's probably faster to blow the gargantua up than keep retrying until he makes it outside. He won't go near the spiky plants very often, anyway, unless you go down near the fallen spire to lure him over (and then quickly run back up onto the hill).
Go into the gargantua's lair and check the back wall for a small cave that you can enter to find a few supplies. On the opposite side of the lair is a large opening in the wall with some yellow crystals past it. Carefully crouch-walk (SRC: crouch-jump) your way up the side of the smaller of the two big rocks under the opening, then crouch-walk onto the highest point on the bigger rock. From there, you can drop down to a nearby rocky ledge, then jump straight across to the edge of the two-tentacle area.
After using altfire hornets to kill the nearby barnacle, stand still and wait for the two tentacles to settle down. Slowly crouch-walk your way over to the large break in the path that leads around them, then quicksave. You could drop down to find an armor battery and three sets of hand grenades on the ground below, but that won't be necessary unless you're out of hand grenades (which you shouldn't be).
Throw a hand grenade so that it explodes over on the other side of the tentacle pit, then quickly jump over the path gap and start crouch-walking along as fast as you can. Hopefully, you'll be able to go on past the third tentacle without any trouble. If not, toss another grenade to help distract it, then run past it. Move on past the tentacles' area to find the area with the exit teleporter.
Before you go for it, use hornets to sneak-shoot both of the alien grunts that are near it. One is in plain sight in the middle of the area, and the other is hiding behind the large rock over to the right. After they're down, look for a health pack behind the large rock, an ammo canister next to the teleporter gadget, and an armor battery next to a small rock near the teleporter. When you're ready, enter the teleporter to be taken to section c4a1c.
Section c4a1c: GRUNT FACTORY, PART 1
Find the passage that leads from the room you start in to a large factory area where peaceful vortigaunts are working. They'll leave you alone if you don't damage any of them or use any weapons at all, including banging on anything with the crowbar.
As you enter the room, turn right and drop down to a slightly lower floor to find a health pack and a bullet clip. Crouch-walk your way out of there, then cross the room to where a lift is slowly going up and down. When it's on your floor, get on it and wait for it to go up to the next floor. Get off and head down the walkway to the right to find a healing chamber that you can stand in.
Return to the lift and wait for it to go down to the bottom floor. Jump onto the part of it that connects it to the pole, then ride that up until you're next to a conveyor belt. Jump to the belt, then ride it to where you can get onto the ledge that goes around a central support pillar. Crouch-walk carefully over to where you're next to the other conveyor belt, then wait until right after two close-together barrels go by before you get on it.
Quicksave when you get near the end of the belt, where barrels are dropped into a liquid. When you go over the side, start leaning on the "Move backward" key so that you'll land on a ledge instead of in the toxic liquid after you fall into section c4a1d.
Section c4a1d: GRUNT FACTORY, PART 2
As soon as you land on the ledge, strafe left and run forward so that you drop down to the floor below near a big barrel. Crouch-walk past the right side of the barrel (or run past its left side if you can) to get to a dark corner where you'll be temporarily safe. Get out the hornet gun and start firing some hornets so they'll hit the nearby alien controller. You may have to move around in your dark corner to see it, but don't let the nearby up-and-down piston squash you. (SRC: As with all controllers, this one will come right up to you, so quickly kill it with the assault rifle or shotgun.)
Crouch-walk up next to the barrel so you can peek around the corner to the left and hornet-shoot the vort that's on your floor nearby. Try not to let it zap the barrel that you're next to, since most of the barrels from here on will contain alien grunts that will immediately become active once their barrels are destroyed.
After that vort is dead, go down to the other end of the area to find a dark room with two more grunt barrels in it. In the back right corner of the room is a narrow passage leading to a dead HEV guy with two armor batteries near him. At the other end of the room is a slightly higher floor you can jump onto to get an ammo canister. Before you do, fire hornets into the big dark pit past the floor to kill an alien controller that would have risen up to attack you. (SRC: Go up to the edge of the pit with the assault rifle out so you can quickly kill the controller with it.)
After you get the ammo canister, go to the left to find a healing chamber. Use it if you need it, then return to the room with the big barrel drop-down pool. Find the small corner lift that's on the floor next to the left side of the pool. Quicksave before you ride the lift up, since there may be a vort or two on nearby walkways. If so, quickrestore and hornet them from down below before riding the lift again.
At the top of the lift, skip a long and alien-infested area by moving onto the barrel drop-down tank's rim instead of the walkway. (SRC: The lift will go up and down, making it trickier to get onto the tank's rim. Also, a barrel will squash you if it drops while you're moving along the back of the rim.) Move over to the left end of the back rim, then take a running jump across to the rim that goes around the leftmost of the two vigorous up-and-down piston things. From there, it'll be easy to jump (or ride the piston) to the walkway on the left.
NOTE: Yes, you could have done this when you first dropped into the area, but it would have been a lot harder due to the nearby enemies, and you'd have been passing up some ammo and armor batteries.
Look around for vorts to kill, then go over to the up-and-down piston in the nearby corner. Get on it when it's in the lowered position, then ride it up and get off on the upper walkway. Go down the narrow, dark corridor until you get near the doorway that's mostly blocked by a grunt barrel. There's a vort just to the left of the doorway, so sneak-shoot it with hornets.
If it runs out the doorway on the opposite side of the room, go back down to the up-and-down piston and look around the corner to see that vort and another one on the walkway. Quickly hornetize them, then go back to the grunt barrel doorway. (Note that even if the first vort doesn't run out to the walkway, there will probably be one out there, so go get it. Also, watch out for vorts on lower walkways.)
Crouch-walk slowly through the doorway gap to the left of the barrel, firing hornets to the left as you go. You should be able to kill at least another vort and an alien controller without having to go very far past the doorway. Once that's done, retreat back through the doorway and look straight across the room through it to see a nearby grunt barrel.
There's another vort hiding behind that barrel, and the best way to get it is to destroy the barrel. Move to where you can only see the right edge of the barrel, then bust it open with altfire hornets and quickly strafe left a bit. Do your best to sneak-shoot the grunt and the vort with hornets without them seeing you. If they do see you, the vort will probably run out onto the walkway, and the grunt will most likely run around in the room.
After they're down, repeat the barrel-destroying and grunt-horneting process with the two grunt barrels you can see a ways farther into the room. With those barrels out of the way, you can see to shoot a couple more vorts down. There's one more grunt barrel way down at the other end of the room that you can see to shoot if you use your flashlight. Use hornets to clear that end of the room the best you can, then quicksave before heading down there.
There's probably another vort or two, and possibly another alien controller, down at that end of the room, so be ready to quickly hornet-shoot them while dodging for cover. After you clear the way down to a doorway on the left, shoot hornets through it to take down the controller in the hallway past it (plus any vorts and grunts that may have run in there).
Now you can relax and check all the dark alcoves in the room for supplies, including tripmines, C4 satchel bombs, health packs, and AR grenades. At the other end of the hallway are several grunt barrels. You could easily bust them with altfire hornets and sneak-shoot the grunts like you did before, but a better way is to set a C4 satchel and a couple of tripmines close to the first barrel, then leave the hallway and detonate the satchel. To make sure both grunts die, you could first jump-toss another C4 satchel so that it lands on the floor behind the second barrel.
After the doorway past the grunt barrels is clear, crouch-walk up to it and start firing hornets at the two controllers that are just past it. Strafe for cover when necessary and keep firing at the controllers until they're both dead. Quicksave, then strafe into the room and start firing hornets at the two vorts. You may have to move around in the room and use the barrels and pillars for cover, but it should be pretty easy to kill the vorts without getting hit or having to destroy the barrels.
Go get the ammo canister that's to the left of the healing chamber, then stand in the chamber if you need to restore health. When you're ready to go, find the three little holes in the wall a ways to the left of the healing chamber and crouch-walk through any of them. Turn right and move along until section c4a1e loads.
Section c4a1e: HUGE SHAFT AREA WITH WAY-HIGH TELEPORTER
Approach the shaft on the left and drop carefully onto one of the two top-level bars in the shaft. From there, drop to one of the mid-level bars, then one of the low-level bars, and then to the shaft floor. Crouch-walk into the tunnel in one corner and move along until you come to two holes in the wall with drop-downs just past them. Move up to the right hole, get out the gluon gun, and quicksave.
As soon as you drop down, turn right and run along the ledge you're on until you reach the back, where you can hide from all the nearby vorts behind a big pillar. You can't hide from the three alien controllers, so quickly blow them away with the gluon gun as soon as you see them. It may help to move around a little on the ledge, but don't let a vort zap you while you're doing that.
SRC: Things will be way harder, and not just because the controllers will charge you. You probably won't be able to make it to the pillar unzapped, and several vorts will be able to zap you long-distance. Plus, two will come along the walkway after you. The thing to do is get behind the pillar and move up against it ASAP, then quickly locate and blast any vorts that can zap you there. After you deal with them and the controllers, the two vorts that are coming along the walkway will probably be close, so kill them with the assault rifle. Quicksave, then peek out and use the hornet gun to take down any other vorts you can see nearby, including the ones on the two spinny lifts.
After all three controllers are down, switch to the hornet gun and stand behind the protective pillar to where you can hornet-kill the vort that's on the nearby spinny up-n-down lift. Then move out to where you can fire hornets up at the nearest higher floor with a grunt barrel on it to see if you can kill the vort up there. Also, jump up and down near the pillar to see if you can hornet-shoot a vort on the walkway that's just above you. (If not, you may have to move away from the pillar until you can see the vort.)
After those vorts are dead, start moving along the ledge that goes around the area. As you go, keep an eye on the floor with a grunt barrel on it. When you get about halfway around the area's ledge, you'll be able to see a dark recessed area with two little pillars under the barrel's floor. A vort is hiding a bit to the right of the right pillar, so sneak-shoot it with hornets or the crossbow before it can see you. Use the flashlight to watch it carefully, since it may run out onto the ledge after you, or go up onto the floor with the barrel. Quickly use hornets or the .357 to finish it off.
Go into its dark recessed area to find a ramp that leads up to the grunt barrel's floor. Now that you're up there, you'll need to start worrying about the vort on the next spinny up-n-down lift, plus two that are on the walkway that's a ways above you. One of those two is probably standing next to the grunt barrel that's near the top of the lowest spinny up-n-down lift. If so, get to where you can see and hornet-shoot it by jumping up and down. As for the second vort up there, it'll probably have to wait. (Though look for it next to a barrel over near the top of the second spinny lift.)
If you follow the ledge that's against the wall, you'll find a room with a healing chamber in it. However, there will almost certainly be at least one vort in there, so approach the room cautiously and with many hornets fired ahead of you. After healing up, go over to the nearby spinny up-n-down lift, then quicksave before you ride it up.
There's probably at least one more vort up on the walkway that the lift takes you to, and you'll want to memorize its position, quickrestore, and take it down with hornets. No matter where the vort is, you should be able to jump-shoot hornets at it from somewhere on your floor, or at least hit it with a carefully lobbed AR grenade.
Ride the spinny lift up, turn to where you can run from it to a little stick-out ledge near a grunt barrel, then run along the main walkway until you get to a large area behind three huge pillars. That's a great place to hornet-shoot the three new alien controllers from, since there's plenty of room to maneuver and no pesky vorts to bother you. (SRC: Use the assault rifle on at least one of these controllers to avoid running out of gluon gun ammo.)
Before you ride the next spinny up-n-down lift in the series, you should carefully walk along the skinny, curving walkways that lead to two small door-sized holes in the wall. Go through the right-hand doorway and down a short red-lit corridor to a doorway that leads into a very tall spiral-screw-style room. Each floor on the central structure has a grunt barrel attended by a vort, and you'll want to get rid of them so you can loot the joint in peace.
Move through the doorway until you can look down and see the top of the grunt barrel on the central structure's lowest floor. Altfire-hornet that barrel to pieces, then quickly back up and fire hornets so they'll swerve down and kill the grunt. You'll then want to hornet-kill the vort that's down there, but it tends to hide behind the central pillar, so you may need to move out to where you can see it before you can shoot it.
Now for the floor that's directly across from your doorway. Move so that you can only see the right side of the grunt barrel, then alfire-hornet it to pieces. Strafe left a bit, then start firing hornets so they'll hit the grunt. After it's dead, look for the vort. It may be hiding behind the pillar, so jump over to its floor and go slowly around the pillar, ready to quickly altfire-hornet it when you see it.
You can now claim the goods from that floor and the floor below. To get to the floor below, drop down onto the spiral walkway that leads to it. To return to the second floor, go up the walkway to where you can jump (or long-jump) to the second floor. Next, move along the walkway to where you can jump up and down to see and kill the vort on the third floor. (No need to break open the grunt barrel this time.) Check the third floor for supplies, then go up the spiral walkway until you can jump-hornet the vort on the fourth floor.
Save before you walk onto the fourth floor, since doing so will probably get the attention of one or more of the three alien controllers who are hiding in the dark areas above. You might want to just pass up the fourth floor, even though it has health packs and armor batteries on it, and an ammo canister behind the two grunt barrels. (SRC: There aren't any controllers up there, thank goodness!)
If you must get those goodies, quicksave, then run get them as fast as you can. Run to the start of the spiral walkway and drop down to the floor below, then repeat the process to get back down to the second floor. Run over to where you can jump to the nearby doorway, then go around the corner past it to be safe. Return to the main chamber and go over to the next spinny up-n-down lift.
Quicksave before you try to ride it, since this lift is a major pain. The first problem is that it doesn't pause hardly at all in its lower or upper positions. You'll need to quickly jump onto it the instant it stops next to you, then hope you're facing the right way to jump off when it stops again. Add to that the chance that the lift will glitch-jam at the top and start damaging you (see the "Starting Tips and Notes" section for more about that), plus the fact that three more alien controllers will appear and start attacking as soon as you ride the lift up. (SRC: This lift pauses like the first one does, and it won't ever glitch-jam you.)
The best way to handle this is to jump on the lift, let it rise to the top, and quickrestore if the glitch happens. Once you ride the lift up without it glitching, stay on it until it goes down again. Jump toward the big area behind the three huge pillars and take cover there. It was a great spot to hornet-shoot the last three controllers from, and it'll work just as well with these three. (SRC: It's better to ride the lift up and enter the side area with the healing chamber, then blow away controllers as they follow you in there.)
After they're finished off, return to a spot next to the lift and quicksave again. Keep riding the lift up and trying to jump off onto the nearby walkway (and quickrestoring when you fall or get glitch-stuck) until you make it. Check the little side area for a healing chamber, then stand in the side area's doorway and look toward the final spinny up-n-down lift in the series. If it still has a vort on it, hornet-shoot it to death.
Go over to the lift and get on it when it stops next to you. No need to rush on its account! Wait until it stops near the big twirly spinaroosa teleporter gadget, then jump into the gadget's zappy green center to be taken to section c4a1f.
Section c4a1f: TELEPORTER TO ENDGAME BOSS
This is just a big platform jump-a-thon. You don't even have to do any long jumps. Just keep taking running jumps to the nearest platform until you make it all the way to the big floating rock with the weird red teleporter swirl on it. After quicksaving, jump up to where you can enter the red swirl, which will take you to the "Nihilanth" chapter.
Section c4a3: DESTROY NIHILANTH
As soon as this chapter loads, start leaning on the "Move backward" key. Release it after your view starts to fade in, then run forward to the base of the large spiky rock that's almost directly in front of you. If you're fast enough, Nihilanth won't get a chance to fire off anything at you before you're hidden from his sight. If he does fire off a teleporter orb, you'll need to shoot down the vort or controller that appears nearby (or quickrestore and try hiding faster).
Look around high up on the walls of the chamber for glowing yellow-orange crystals. There are three of them, though your view of one of them may be partly obstructed. If you move around carefully behind your protective rock, you should be able to see and shoot all three crystals without Nihilanth seeing you. (I prefer to use the crossbow for this, since it just takes two quick darts to blow up each crystal. SRC: Four darts per crystal.)
That did away with Nihilanth's ability to draw power to heal himself, so start blasting him. Edge carefully over to where you can see and shoot one side of his huge head without him seeing you. Don't use any RPG rockets yet, but feel free to empty the gluon gun, .357 Magnum, and crossbow into his head. You could just use alfire hornets, but there's no reason to conserve ammo now -- this is the final battle of the game!
Shoot his head until the top of it opens up, then keep shooting it as long as he keeps moaning or growling occasionally. After that stops, get out the RPG and quicksave. It's possible, though rather tricky, to hit Nihilanth's exposed brain spike from your hiding place with a rocket. Keep firing rockets and swerving them into the approximate center of the top of Nihilanth's head until he starts spinning around and spewing out colorful energy, or until you run out of rockets.
If you ran out of rockets, quickrestore and try again. If you get him to start spinning and spewing, and the game never teleports you to the "Endgame" chapter (a common glitch), quickrestore and try again. If the glitch keeps happening, or if the rockets never seem to work for you, use the whoosh-thing on the ground a ways to the right of your rock to fly up over Nihilanth's head. Look down and shoot his glowing brain spike with the assault rifle or some other gun, or land on his head and beat on his brain spike with the crowbar. That should always work, and get you teleported to the "Endgame" chapter. (SRC: Neither the rocket strategy nor the crowbar will work, so you'll need to whoosh up and shoot his brain spike with something.)
Section c5a1: G-MAN FINALE
There's not much to do in this "chapter," since that aggravating G-Man jerk steals all of your weapons and uses his freaky, inhuman powers to teleport you around while talking to you. Wait until you're in the tram car and he says it's time to choose, then either go through the tram car's door and enter the big portal, or just wait until you're put in an area with lots of alien grunts. Either way, the game is over.