Antichamber is hard to explain to someone because it is hard to explain the non-Euclidean geometry the game is based on.
While games like Everything and Ultraworld make you think about the nature of existence in abstract ways, Antichamber makes you live through an abstract existence in practical ways.
For instance, in the above trailer, the player is shown red stairs leading down on their left and blue stairs leading up on their right. However, both somehow loop back around onto the room you start in.
Looking at different sides of the same cube can lead to completely different rooms. A glass pane can show different colors from different sides. Pressing your face up against it so that you only see the represented color changes the whole world to be that color.
These are both early puzzles that set the tone for the Alice in Wonderland-esque puzzles seen throughout the game.
Antichamber is available via Steam for PC, Mac, and Linux for $19.99.