I saw this doc last night and found it to be amazing.
Urban Explorers: Into the Darkness
(For those of you with Netflix: streaming)
When I was a kid I used to explore all kinds of abandoned buildings and tunnels, so that was one reason I really liked this film. Also, these folks who make a hobby out of exploring urban environments take some amazing pictures and just a handful of shots is enough to give you tons of ideas for any modern or fantasy game.
Check it out.