Gorogoa rocks.

If you want something more trippy, here are a few puzzle games to try:

• Bridge - MC Escher-esque, non-euclidian geometry
• Manifold Garden - you change gravity
• GNOG - “tactile” puzzle that’s really quite odd
• Antichamber - non-euclidean geometry

Each of those are quite good, and a bit more of an “LSD-trip” than Gorogoa, and you can go further down the rabbit hole if you search for “psychadelic games” or similar.