Aliens vs Predator 2 singleplayer custom map titled "Shafts".
Map author: Phil 'Windebieste' Wlodarczyk
Shafts is a marine based skirmish map that takes place in a Giger-looking skyscraper environment. The player must evade enemy aliens while scaling across the chasms between the the skyscraper/shafts. This is one of the most frustratingly hard skirmish maps because player movement is severely limited. The player is mostly forced to go in one of two directions on most platforms. Furthermore, many of the spawning aliens land right on top or near the player. They can easily gang up and corner the player, making survival very difficult.
I actually love the multiplayer version of this map as it is fun to watch players falling down the chasm. The skirmish version is a bit too frustrating for me personally. Perhaps if the npcs were changed to humans or predators that could easily fall off platforms it would be much better.