The Waterworks

A 1995 WAD for Doom 2 according to the file timestamp, and there are definitely a lot of 1995 quirks. Missing textures that are pretty easy to spot, like a "lift" where the red key is, some confusing level design, and one moment where you can't finish the level because a Cacodemon would permanently close the door you need to enter to complete the level. Perhaps the oddest, although kind of funny, thing about this WAD is how most of the secrets are just small sectors you just need to stand on, and you'll quickly know what they are with the help of the automap (Those 17 secrets don't seem daunting anymore). You can play a lot worse when it comes to old levels, but The Waterworks isn't something that stands out from the bunch.