Teufelsberg, Berlin, Germany by EmmaJG on Flickr.
Via Flickr: Teufelsberg (German for Devil’s mountain) is home to an abandoned American/British Cold War listening station. The hill itself is made of World War II rubble, piled on top of a never completed Nazi military college (Wehrtechnische Fakultät) designed by Albert Speer. The building was so hard to destroy that it was easier to bury it instead. Operations on “the Hill” began in 1961 after it was discovered that it was a great spot for listening in to Soviet communications, and continued until the fall of East Germany and the Berlin Wall.