Book: Access All Areas.

Currently reading: 'Access all areas: A user's guide to the art of urban exploration', by Ninjalicious.

Urban exploration is basically hiking in the middle of a city, exploring abandoned buildings and the detritus of the urban landscape, infiltrating access tunnels and 'employees only' zones. The book is mostly a safety guide, but also covers topics such as not getting caught, and convincing security guards to let you go. Sounds like fun to me.

Ninjalicious is the founding member of a group called Infiltration. They have a website here. This was brought to my attention by my friend, Mr. A.