Aliens vs Predator 2 singleplayer custom map titled "Timebomb".
Map author: Artalavista
Timebomb is one of the best horror based singleplayer custom maps out there. The concept of the map is simple; you are stuck in a spooky subway with a bomb set to go off in five minutes (once you walk past the red laser wires). There are two ways to complete the map. The first is making it to the apc, while the second is defusing the bomb itself.
While it is a short map, it is quite excellently made. It has a very creepy atmosphere with a ton of custom textures, skins and sounds for added effect. The added tension of the bomb going off makes it even better. Unfortunately, Artalavista left one missing texture in the map that sticks out at the start on a door. However, this doesn't ruin the map at all. I highly recommend this one if you enjoy the scarier AvP2 maps.