At the height of the Cold War, a hill in West Berlin known as Teufelsberg (Devil's Mountain) served as the perfect spot for U.S. and British intelligence agents to turn an ear on East Berlin and Soviet communications. In its glory days, state-of-the-art listening towers and rotating antennas at the Teufelsberg spy station exposed the Communist Bloc's secrets to analysts and linguists from the U.S. Army and the U.K.'s Government Communications Headquarters. After the fall of the Berlin Wall, Teufelsberg was abandoned to decay, graffiti artists and weekend partiers. The U.S. Army Security Agency (ASA) began its first SIGINT operations at Teufelsberg in 1961 after discovering that the 380-foot hill offered unobstructed collection of communication signals. As the facility grew and more buildings were constructed, the U.S. National Security Agency joined in on the spy operations. Photo: Matt Biddulph/ Flickr

Another view of what remains of the main listening tower after years of neglect. Photo: Vic Bergmann/ Flickr

An aerial view of Teufelsberg during its glory days at the height of its spying powers. Photo: Chaos Computer Club

Referred to by the Allies as The Hill, locals preferred to call the main listening tower and radomes "Berlin's Balls" — for obvious reasons. According to a former U.S. Army linguist once stationed at the site, the listening station was subject to high winds, due to its height. The fabric domes were kept inflated by internal air compressors to counteract the winds, but sometimes failed at this task. When that happened, a klaxon would sound an alarm to warn

workers to get out from under the dome, lest it collapse on them before the compression could be increased. "The air pressure inside the dome was sufficient that technicians who from time to time had to work in the dome had to decompress on exit to prevent the bends," says Lew McDaniel who worked as a Russian linguist at the site from 1968 to 1971. Photo: Axel Mauruszat

Access to Teufelsberg was restricted after its closure, but this, and the double fence surrounding the site, hasn't stopped graffiti artists from invading the grounds and turning them into an art project for free expression. Today you can take an organized tour of the site. Photo: Vic Bergmann/ Flickr

Even the hallways at Teufelsberg have been tagged by graffiti artists. Photo: Vic Bergmann/ Flickr

High up in Teufelsberg's towers you can still hear the sounds of surveillance whispering in the wind if you're quiet. Photo: Vic Bergmann/ Flickr

The view from inside one of the radomes where a 40-foot rotating dish antenna once stood. Local lore has it that each year in the summer during the annual German-American Festival held nearby, the Teufelsberg spooks noticed that their reception of radio signals mysteriously improved. They eventually figured out that the Ferris wheel erected during the festival served to amplify the signals. Thereafter, they made arrangements with the festival organizers to keep the wheel in place for longer periods of time after the festival closed. Photo: Vic Bergmann/ Flickr

Vandals and the natural elements have contributed to the decay of the bottom floor of this snoop tower, leaving little but the entrance frame standing. Photo: antenne/ Flickr

After the U.S. and Allies abandoned the listening station, there was talk of turning it into a spy museum or building a hotel or exclusive apartment complex on the spot. The latter prompted cries of protest from weekend ramblers who have come to consider the site a volkspark of sorts. More recently there's been talk of tearing down the buildings altogether and re-foresting the hill. Photo: parkinpants

Graffiti in Teufelsberg's chow hall calls to mind the east-west space rivalry that existed for years until it ultimately ended in détente with the International Space Station collaboration. Photo: Steve Jackson

The Allies abandoned Teufelsberg before the U.S. had a chance to finish construction on this unidentified building. Photo: Steve Jackson

Teufelsberg isn't a natural elevation but is a man-made hill built after World War II with rubble carted out of Berlin from the city's bombed-out ruins. Prior to the war, the site was slated as the location for a Nazi military-technical college designed by Albert Speer, but the Nazis failed to complete construction before war broke out. Photo: Vic Bergmann/ Flickr

A bucolic pathway leading up Devil's Mountain recalls The Hill's post-war days as a popular ski run before the spooks took over the location with their spy tools. Today locals still use the old pathways to ski or toboggan down the slope. Photo: Vic Bergmann/ Flickr

Detritus of vandals and thieves is strewn in the hallways of spookdom. Photo: Gregor Fischer/Flickr

On a clear day, the listening post's elevated vantage point in West Berlin gave spooks a beautiful view over the nearby Grünewald forest. Photo: Vic Bergmann/ Flickr

A sentry box built to discourage the trespassing of curious Commies and others can't keep out the tag artists these days. Even the locks and fences securing the 48-acre site have proved to be useless against copper-cable thieves and others who have stripped the site of any valuable materials that remained after the spies left with their equipment. Photo: Matt Biddulph/ Flickr

The site has become a popular weekend haunt for day trippers willing to squeeze through fences and scale rickety scaffolds. Photo: Matt Biddulph/ Flickr

A window view from one of the towers shows the straight shot spies had to communication signals in the east. Photo: parkinpants