What's quite dark, VERY smelly, and is a breeding ground for some B-movie monsters?
Simple. It's Floaters! One of my completed maps that's just been sitting around with a dumb look on its face, set in a vast network of sewers. I'm finally dusting it off and releasing it. I've strewn about a large amount of MP5s as per the request of my fellow CHZers, and (reluctantly) included the crossbow, although you have to go for a swim to get it (ew).
While it's no Antareus Core, it's still quite fun, and watching someone fall into the River O' Poo while they're trying to blow off your head is funny.
River O' Poo is (c) Victor-933