Beyond Perception is a mind-bending Gamejolt dig that I found yesterday that was made using the Unity engine. You start out in a room filled with museum paintings. Stand on a square in front of one of the paintings, and you are instantly teleported into the painting. However, the room is actually just the painting rendered in 3D, so when you're looking around, parts of the room not seen in the painting are the same color as the background, making them nearly invisible. This leads to some confusion on where the floor, ceiling and walls are. This game is a serious challenge, and requires that you look at each of the rooms from a lot of different perspectives--literally. Most of all, for this game you must suspend your disbelief and forget what you know about reality. This mind-boggling game will leave you speechless even after the first level. You can get the the game for free here. Good luck!