It's a lot easier to get artifacts from the castle. If you cross the dining room, and use the staircase that is now open to you on the left side, you have a couple floors of baddies to demolish. You have to solve puzzles mostly, to get at the artifacts, although on one occasion there is just a baddie to kill for one. Mostly though, the puzzles are inventory based, and kind of fun. Maybe the prince doesn't appear until you do some damage to all these folk, I don't know...
"How could drops of water know themselves to be a river? Yet the river flows on."
- Antoine de Saint-Exupéry