To most people, it looks like a regular graffiti wall. But to bunker fans, it’s the flak tower sticking out from the top of the Big Bunker Mountain.

The Big Bunker Mountain is located in one of Berlin’s most popular parks, Volkspark Friedrichshain. Situated just a short distance from Alexanderplatz, it’s a gathering place for exercisers, families with children, dog walkers and anyone who seeking an escape from the hectic intersection of the Mitte and Friedrichshain districts.

The park truly looks like a fairytale. At the entrance, on the corner of Am Friedrichshain and Friedenstraße, you are greeted by the Fairytale Well, a fountain featuring characters from the Brothers Grimm stories.

During World War II, the park was turned into a military zone. The second of three flak towers was built there from April to October 1941. It protected against bombers with four heavy 128 mm guns and twelve 20 mm light gun.

Like the flak tower in Humboldthain, the flak tower in Volkspark Friedrichshain was destroyed when the war ended. The command tower that sent signals to the semi-automatic guns on the flak tower was also destroyed.

The flak tower was demolished in 1946. The Soviet army put 40,000 kg of explosives in four ammo chambers at the bottom corners of the tower. The blast blew out the bottom floor on all sides, making the five-story tower one floor shorter. The tower also split in half.

After that, 3,000 women called Trümmerfrauen (rubble women) spent four years covering the ruins with rubble from the destroyed neighborhood. They also made paths and planted trees on the hill.

Today, the big hill is called Big Bunker Mountain or Mont Klamott, and the smaller hill with the command tower is called Little Bunker Mountain.

Even though the cracked flak tower is covered, there is one spot where the bunker can still be seen. It’s hard to notice, and every day joggers pass by without realizing it is a Nazi bunker, a reminder of a past we should not return to.

Before you get to the top of Big Bunker Mountain, you’ll see a piece of concrete covered in graffiti. That’s what’s left of the flak tower. In the old photo higher up in the article, it’s the small triangle pointing up in the center.