Here are a few I've found which investigate and explain all of the hidden bits of Europe during the cold war. Many locations are now demolished or redeveloped and these site are a historical link to an interesting period of history. http://www.lostplaces.de/ In German, but an English translation is due soon. Take a look at the listening posts on the old inner German border. Discreet. Not!! http://www.bunkertours.co.uk/ Excellent BRIXMIS link. http://www.subbrit.org.uk/ Underground hidden things. I have more links at work and I will post them soon. Its an area i find interesting as many of these places I had heard during my time in Germany in the 80's but never got to visit or see.