Ian MacLarty's Catacombs of Solaris [Itch.io page] isn't really a game so much as it is an endurance challenge which has mated with a Magic Eye picture or something. It made my eyes feel like they wanted to crawl out of my face and die as well as being really interesting from an optical illusion standpoint.
Catacombs of Solaris is fascinating in that it creates the illusion that a path will take you one way because of how the panels which line the walls use linear convergence. It makes the space look like there are tunnels carrying on into the distance because there seem to be these vanishing points which normally denote a path you can follow towards said point. But it's only by moving around the space that you can discern where the real path is - it's the motion which reveals what is a flat perspective illusion and where the real tunnels are.
There are no objectives other than MacLarty inviting you to find the room you like best, so you're not questing after a particular objective, just seeing what you get out of the experience.
For me it's a curious, really well-executed riff on perspective and exploration to create these horrifically confusing catacombs. It's also the sickest I've ever felt in a game outside VR - the colours and the disorientation and the way you have to look in order to work out the space... Whole worlds of NOPE. I haven't stopped wanting to scoop my eyeballs out of my head since playing it just so I can get rid of the feeling that they are having some sort of freakout inside my face. It's like having a hangover without so much as a snifter passing your lips.
I don't think I've made this sound fun at all. But it is interesting and pay what you want on Itch.io.