Void 1.0

DOOM is one of the oldest FPSes in existence, and its engine is famously so robust that it can run on pretty much anything and also create pretty much anything.  From FPSes to RPGs to companions to a city living game, it has a ton of different mods that can all do different things. One of the best ones out there is Void, a map that really pushes what a map can look like.

To install Void, you need to have ZDoom and move the WAD file into the GZDoom folder, which is pretty par for the course for DOOM mods.

The setting is unique as far as DOOM goes. At first, it sounds typical - science experiment opens a portal into another dimension. Only this time, it isn't a portal to hell. It's a portal to a surreal, insane dimension. The visuals are incredible as far as DOOM maps go, with a ton of scenery that would not look out of place in a lovecraftian dimension. This map changes so much that it's highly recommended you read the txt to start. There's a ton of information in there that the game won't tell you about. 

There is some fighting, but puzzles, death traps, and platforming takes the forefront here. This is an incredibly unforgiving map, and you should save often because you may die without warning at any point. There is a ton of tight platforming that is incredibly easy to die on.

If you can look past that, though, then Void is one of the most unique maps out there.