Bless map editors. They make wonderful things possible—wonderful things that normally couldn't exist.
These maps hail from franchises like Call of Duty, Battlefield and Counter-Strike. The one above is Nuketown. Here are the rest:
There is one more map to check out, here.
This looks really rad—if I was playing Far Cry 3 on PC, I'd play these. Alas, console gaming. I can't even take the HUD off my copy of Far Cry 3... not yet, anyway.