Sometimes, when I'm playing a game, I can't help but wonder, "What were these guys smoking in order to come up with this stuff?"
Here are some of my favorite examples:
-Rainbow Road from Mario Kart: You're on a rainbow. In space. While creepy neon lights in the shape of other characters show up in the background. It was pretty messed up.
-That flower level in Paper Mario: Oh god, do I really have to explain this one?
-Pokemon Pearl: Not so much a trippy moment, more like an extremely trippy cast of characters. I mean, look at this monstrosity:

WHAT. THE. ****.
So, what do you think are the trippiest moments in gaming history?
EDIT: My list will probably change drastically once I play Super Mario Galaxy, but whatever.