Espionage enthusiasts, look no further. Inside Grunewald, a forest in Berlin’s west end, there is a former NSA field station, once run by British and American intelligence officers during the Cold War. Teufelsberg is at the highest point in the city of Devil’s Mountain, which is made of World War II rubble. Built in 1936 and run until the 1990s, Teufelsberg was meant to be a Nazi military-technical college. In 1963, construction began to build the listening station in the former British sector. Since the fall of the Berlin Wall, German authorities took hold of the offices. It feels abandoned, covered in graffiti. Walk through former security officer’s offices, look through broken glass windows. One former intelligence officer with the U.S. Army Security Agency gives tours on weekends for a reasonable price. Wear boots, the walk to the top is 30 minutes.