Great moments in PC gaming are short, bite-sized celebrations of some of our favorite gaming memories.
People remember Doom for being groundbreaking, but it's easy to forget how ahead of the curve it really was. Just look at the secret level of Episode 3, which was getting meta on the FPS genre before it even really existed. It's called Warrens, and it's a great big joke on you, the player, of a kind that might not seem that big of a deal now, but was a huge shock back in 1993.
The gimmick is that when you reach it, you get a real sense of déjà vu. It's exactly the same as the first level of Episode 3, Hell Keep, with the exception of the name. The trick is that when you hit the exit the walls promptly fall down, you get mugged by a rocket-shooting Cyberdemon, and have to backtrack through the whole map again with newer, tougher enemies all the way down your route. A genius moment of level design, made all the more effective by the fact that this was pre-internet and so the moment was unlikely to have been spoiled in advance.
This is only one of many such moments in the original Doom, part of what made it a design milestone as well as a technical one. Probably the subtlest is how the second chapter, The Shores of Hell, finishes on a map called Tower of Babel, which is slowly built over the course of the chapter as you complete the earlier levels. Then of course there are sequences like tripping a trap and having an army of demons teleport in out of nowhere, discovering enemy in-fighting for the first time, or, in the sequel, suddenly finding yourself in id Software's previous game, Wolfenstein 3D. But despite all that cleverness, the reveal in the Warrens remains one of the best early gotchas in shooter history, and well worth the jump.