http://www.pendar.pwp.blueyonder.co.uk/Tube/

http://www.subbrit.org.uk/sb-sites/sites.shtml

Here are some more site you may find of interest.  The first is the London Underground

Second is mainly "Cold War" bunkers etc.   All very interesting but also very ilegal to enter without the proper permissions. 
 

 ecurb - The Devil