This map is a zombie horde experiment with random triggers.
The maze randomly sets itself on level load and all the corridors look the same, so it's an 'old-school' dungeon-like design that's realy easy to get turned around and lost in.
The zombies are all set on random triggers so sometimes a corridor will drop them out of vents from the ceiling and sometimes that passage will be clear only to send a horde charging at the player around the next turn, or a random wall section will open up allowing giant baddies to jump you. Fun stuff!
The map itself took only 1 week to make due to the simplicity of it's geometry but the complex kismet involved in setting up the hundreds of random triggers took another week, so total time to build was 2 weeks.
Here are a few screenshots to give an idea of the atmosphere. (click image for 3360x2100 version)