Teufelsberg in Berlin is a man-made hill on which the US NSA built one of their largest listening stations in 1963 as part of a global network of surveillance. It was known as "the Hill" by the soldiers who lived in Berlin and commuted there from their accommodation.
The site was nearly razed, but was (perhaps temporarily given the rapid gentrification of Berlin?) saved, and today is a wonderful "abandoned - though not really at all abandoned" site to visit, with spectacular views and wonderful art.
