Berlin spent 22 years burying a building it could not get rid of.

That building was the Wehrtechnische Fakultät, a faculty of military technology begun in 1937 as part of Germania, Hitler’s plan to rebuild the city as a world capital. Albert Speer drew it up. War stopped the work and left a concrete shell sitting in the Grunewald forest, and after 1945 nobody could agree on what to do with it. Berlin’s official city portal says the shell was blown up and the site then turned into a rubble dump. Most tours tell it differently: demolition went badly, and burial simply proved easier. Either way, a good deal of it is still down there.

Eight hundred lorries a day

From 1950, the trucks came. The Local, drawing on the Berlin daily Tagesspiegel, puts the convoys at up to 800 lorries a day for 22 years, hauling out the ground-up remains of apartment blocks, churches and factories. City figures put the final pile at 25 million cubic metres. Most other accounts say 26 million, which gives some idea of how precisely anyone was measuring.

Whatever the true number, it topped out at 120.1 metres, the highest point in West Berlin.

Then a million trees went in on top, and Berlin had itself a forest.

Ski jumps and a very bad wine

A city with a brand new mountain will find uses for it. The Local dates the first ski jump here to 1955, with a bigger one in 1962 pulling 5,000 spectators to its opening, and the city’s tourist board, visitBerlin, describes a full slope on the hill complete with drag lift, jump and toboggan run. In 1986, for Berlin’s 750th birthday, they held a ski race down a pile of bombed houses.

Wiesbaden sent a gift of grapevines in 1970, which is how the hill briefly acquired Wilmersdorf’s official vineyard. The Berliner records that the first vintage was christened Teufelströpfchen, Devil’s Drops, and that it was sour. The outlet also notes that the ski lift was later pulled out because its electric motors interfered with radio signals up on the summit.

What sat on the summit

Americans had worked out early that nothing else in the city stood this high, and the extra height gave a clean line of sight over the Iron Curtain. Mobile intercept units took position in 1961 and permanent buildings followed in 1963, as documented by Abandoned Berlin, which has collected accounts from veterans of the site. What grew there became Field Station Berlin: white radomes like enormous golf balls, dish antennas inside them, shift work around the clock, and a standing habit of admitting nothing.

Whether it was radio traffic, microwave links or satellite transmissions, if it crossed the sky over the German Democratic Republic, someone on the hill was probably copying it down.

Who was listening to the listeners

Rather a lot of people, as it turned out. The Stasi Records Archive holds a 68-page East German analysis of the structure and activity of the field station, marked top secret and kept under wraps in German archives until 2011. A related item in the same archive is a photo series, put together for a 1985 student thesis at the Stasi’s own law college in Potsdam.

Some of that material walked out the front gate. James Hall, an American signals analyst posted to the hill in the early 1980s, spent years selling documents to East German and Soviet intelligence. Germany’s Federal Agency for Civic Education describes how a colleague noticed the smuggling, a hidden camera caught him at it, and a sting in December 1988 led to his arrest. A court gave him 40 years the following year.

Every plan since has come apart

Americans and British packed up after the Wall fell, stripped the equipment and left the buildings standing empty. Investors bought the site in 1996 with talk of apartments, a hotel and a spy museum, and the money evaporated. In 2007 David Lynch arrived wanting a university of transcendental meditation on the summit, an episode TIME covered largely because Lynch’s local partner used the launch to call for an “invincible Germany”, a phrase that went down in Berlin about as well as anyone might predict. Permission never came.

Graffiti crews turned up instead, and the towers now hold one of the bigger street art collections in Europe, behind a fence, for a fee.

Speer wanted a monument to the Reich. The NSA wanted an ear pointed east. Developers wanted a conference hotel and Lynch wanted enlightenment, and none of it stuck. What Berliners got and kept is a place to fly kites, ride a toboggan and watch the sun go down, built from the wreckage of their own houses.