Teufelsberg is Berlin’s highest hill, 80 meters above the city. It is artificial and was built by the allies after the second world war, on top of a nazi military-technical college. The US National Security Agency built one of its largest listening stations on top of the hill to keep an eye (and ear) on DDR, Soviet and other Warsaw Pact nations. The station continued to operate until the fall of DDR in 1989. Today its closed, partly occupied by a (really nice) hippie artist family, so you have to brake in at own risk through a broken fence.
View of the city. Berlin’s very own Eiffel Tower in foreground.