Teufelsberg, in photos, is a tall shaft with a ribbed white vinyl covering stretching up several stories between two globes perched on a four-story concrete building looking out over a dense forest. Yes, you could say it looks phallic. In reality, these globes on the roof of a featureless building once shielded the antennas at the center of West Berlin’s Cold War espionage activities. Abandoned by Western military forces in 1992, the complex has become a giant indoor graffiti park, a very cool movie location, and a fascinating excursion for Berliners curious about the city’s espionage past.

It’s a rainy day and I am trudging up to the ominous “Devil’s Hill” in the Grunewald, a leafy forest covering 3,000 hectares in West Berlin. Hitler’s military planned to build a military staff college on the forest floor, but were distracted from the unfinished project after the war started; in 1945, the concrete foundations in the woods proved the perfect place to dispose of the rubble in the city and the ad hoc landfill became an earth-covered mountain 115 meters high.

The height of the hill, post-1945, also made it an ideal spy station for the United States Army Security Agency (ASA), whose main function was to listen to, record, and decipher the military communications of the DDR (East German) and Soviet military forces stationed for hundreds of miles around Berlin in East Germany. Allied forces officially occupied West Berlin from 1945 through 1990, but security matters were their main interest, and under the cover of orbs in the forest, they had discovered the perfect secret spot.

It doesn’t look exactly inconspicuous to the local population: the roof offers a view over the entire city on a clear day. Former ASA Signals Analyst Christopher McLarren, wearing a blue plastic rain poncho, leads me and some other curious civilians in soppy wet shoes and clunky umbrellas onto the rooftop between the giant orbs. He was drafted in Washington D.C. and came to Teufelsberg for his military assignment in the early 1970s; he has remained a Berliner ever since. Lately, he spends his Sunday afternoons telling (declassified) stories about analyzing radio transmissions and avoiding close calls with World War III to anyone ambitious enough to trod through the forest. Although the US and British military keep intelligence files classified for many years, the end of the Cold War and the closing of the base offer a rare peek into the US intelligence world.

“These were real people, and there was real danger. I think it’s useful to know that the world is not necessarily a safe place—yet,” he explains to me when we meet later for Kaffee und Kuchen. Besides, he adds, “the mountain does have a kind of magic to it.”

Like most of Berlin’s Cold War sites, there is a certain resonance with current events that makes the past feel less like a history lesson and more like a foreshadowing. Conspicuous, hilltop antennas may be a thing of the past, but cyber hacks, fake news, and clandestine enemies are the modern security threats that replace them.

Accessible by partially-trodden foot trails through the forest and surrounded by tall fences and “No Trespassing!” signs, the area maintains the allure of the forbidden although a ticket booth, art studios, techno music, and a makeshift coffee shop and bar prove that visitors are anything but unwanted here. (Teufelsberg even has a website.) In 2006, the property was sold to private owners who planned to turn it into a luxury retreat center, but a long-ignored county statute to preserve the Grunewald from commercial development has been vociferously defended by locals since the sale, leaving the site in a public-private limbo.

As McLarren trots up an outdoor stairwell with my group, he describes the nondescript, windowless fortress that he remembers. “We always had the presumption that the other side was listening. You didn’t ‘talk shop’ away from the shop.”

Today, the walls of the same building are open to the outside and the interior has been stripped to its concrete bones. Everything inside is open to the world. The “private ownership” of the site hasn’t stopped graffiti muralists from contributing Berlin’s signature artwork style on a regular basis. Each of the building’s four stories is filled with murals-on-concrete, painted on and painted over at will. It’s like a less-commercialized answer to the enshrined, iconic section of the Berlin Wall left standing in Friedrichshain, the East Side Gallery.

In addition to the East Side Gallery, many clues refer to the Cold War’s modern relevance elsewhere in Berlin. An espionage overview at the German Spy Museum covers the history of human intelligence and communication surveillance, and asks questions about internet privacy and modern data collection. The preserved remnants of the East German secret police, the Stasi Headquarters in Lichtenberg, contains some of the real listening devices and memories of psychological destabilization tactics used by the Stasi to keep track of the movements of DDR citizens.

Nearby, an archive houses the Stasi’s personal files, kept on most of the DDR’s residents and foreign persons of interest. Although the Stasi frantically shredded as many files as possible while DDR citizens demonstrated outside, millions of files never made it to the shredders before the citizen-takeover. The post-reunification government’s decision to open these files allows citizens to request access to their own file, often putting to bed mysteries about their past.

“I put in a request to see mine,” says McLarren, who doesn’t doubt that the Stasi followed intelligence workers like himself. “But apparently some of the first files to be destroyed were those of the foreigners. So if they had a file on me, I don’t know. It was probably the case for everyone, but mine doesn’t exist.”

Remnants of the Stasi’s reach and brutality remind people of the importance of privacy rights and how disastrous it can be when they are degraded. “I think it makes it clear how evil the system was,” McLarren says. “Especially as Americans, it’s a good warning about what can happen if you drift into that sort of thing.” The drift might happen via government-hyped paranoia and strategic fear-mongering, as is on display at the Stasi Museum. “In times of danger, people accept security measures that they wouldn’t otherwise. But security measures don’t expire. They tend to stay and be added to,” he adds.

Today, the ASA is folded into the NSA, which was a separate civilian and political listening agency at the time. (McLarren stresses that the ASA was only spying on the military, to his knowledge.) Although Teufelsberg focused on military listening, it still provides a rare glimpse into the American government’s surveillance activities.

In Cold War days, agents listened to and recorded the enemy’s communications, picked up by antennas inside the golf ball domes on the roof. Inside the windowless building, McLarren and his signals analyst colleagues decoded patterns and interpreted the meaning of the information gathered on the roof. “It was our job to figure out who was speaking and what they were doing. We were learning as much as we could about the other armies, how they were organized, their tactics,” he explains. Much of a signal analyst’s work was the detective work of piecing together small daily facts and uncovering their possible significance. “It was often quite boring, and nothing like James Bond or anything,” he tells the tour group.

I ask him later if he learned anything humanizing about the East Germans and Soviets as a result of his listening. It turns out, in some regards, they weren’t so different from the Americans. “The East German army used to tell Polish jokes about their socialist brothers in arms. The curious thing is, they were approximately the same Polish jokes we were telling in the States at the time.”

Down the hall from the analysts, management and officers met and planned top-secret actions, based on their intel. On the building’s lower floor, a maintenance crew dealt with day-to-day details, like running their own massive shredders and destroying classified items in chemical solutions at a sort of intelligence crematorium on the ground floor.

Despite the heaviness of the location, McLarren says West Berliners, both foreign Allies and locals, felt they were on an “island of relative safety in a very turbulent sea” after the wall went up. Even in 1989, they still felt safe. While anti-government protests of one million people (“That’s one in every seventeen people in the country!”) were raging across the wall in East Berlin, he says, “we were simply observers of what was going on across the way.”

I’m not sure I buy that attitude. In an era of intense suspicion and near-strikes based on mistrust and misinformation, how could West Berliners feel so uninvolved? But in many ways, they were right to feel that way. A lot of what we know today proves that the Cold War was all just posturing, with neither the Soviets or the Americans ever intending a first strike, only preparing to retaliate if a first strike was launched.

“In many ways that was sad to hear,” McLarren says about learning that the Soviets didn’t intend a first strike either. “Because if they didn’t plan to attack and we didn’t plan to attack, all of that suspicion and all of that money and all of that preparation for something that nobody wanted is kind of sad, but I’m afraid very human. Because you can’t fully trust, you can’t know.”

In Berlin, while much has changed, I can never shake the feeling that so much is still the same.