Nemo's base is that place where his office and lab is located.
Exit through the door.
You will then be at the geothermal room.
Climb the stairs at right.
Exit through the door and be at the ramp.
This is where you did the pipes puzzle.
Climb to the end of the ramp and exit through the door.
You should be at the cemetery-vase puzzle.
Climb the stairs again and go through the door.
You are now at the inlet.
No - those are the only 2 endings.

These 2 endings both fulfill Nemo's desire or care of the island.