With some of the more popular destinations for Urban Explorers, you’ll often find that a particular location has been photographed by many different people from many different angles. Microsoft’s Live Labs are working on a bit of technology that takes a large collection of photos of a place and, by analyzing them for similarities, is able to map them to a reconstructed 3D space.
There’s a cool demo here, though it does require you install a new plug-in for your browser to view it.