To the untrained eye, it just looks like a typical concrete wall with graffiti. But to the bunker enthusiast, it’s clear that this is the Friedrichshain flak tower peeking out from the top of the Big Bunker Mountain.

Volkspark Friedrichshain is one of Berlin’s most popular parks. Located just off Alexanderplatz, it’s a gathering place for exercisers, families with children, dog walkers and anyone who needs a retreat from the hectic intersection of the districts of Mitte and Friedrichshain.

The park is literally fairytale-like. From the entrance on the corner of Am Friedrichshain and Friedenstraße, you’ll find the Fairytale Well, a fountain decorated with characters from the Brothers Grimm fairytales.

During World War II, the park was converted into a military area and the second of a total of three flak towers was built from April to October 1941, threatening bombers with fire from four 128 mm caliber guns and 12 light cannons 20 mm caliber shots.

Like the flak tower in Humboldthain, the flak tower in Volkspark Friedrichshain was blown up when the war ended. The radar tower that sent signals to the guns on the flak tower suffered the same fate.

The demolition of the flak tower took place in 1946. The Soviet army had placed a total of 40,000 kg of explosives in the four ammunition chambers at the bottom of each corner of the flak tower. The result was a huge shockwave that caused the buildings around the park to collapse. The bottom floor of the five-story flak tower was blown out to each side, shortening the bunker by one floor. In addition, the flak tower split in half.

Subsequently, 3,000 so-called Trümmerfrauen (rubble women) worked for four years to cover the ruin with rubble from the destruction of the war. They also built paths and planted trees on the hill.

Today, the giant hill is called the Big Bunker Mountain or Mont Klamott, and the smaller hill that hides the light tower is called the Little Bunker Mountain.

But even though the cracked flak tower was covered up, there is one place where the bunker is visible. It’s barely noticeable, and every day joggers run past it without thinking that it’s a Nazi bunker, haunting us from a past we shouldn’t go back to.

Before you reach the top of the Big Bunker Mountain, there’s a piece of concrete covered in graffiti. That’s the flak tower. In fact, it’s the little triangle pointing to the sky in the center of the historical photo further up in the article.