Like most theme parks, Wunderland Kalkar features lots of fun attractions and rides. Unlike the average Six Flags, however, it’s located on the grounds of what was once a nuclear power plant.

Visitors to Wunderland Kalkar don’t seem too bothered by the fact that they’re enjoying a day of family fun on the grounds of a deactivated nuclear power plant, primarily because the park, just outside of Düsseldorf, was never fully operational. Construction began in 1972 but delays and fierce protests from locals and the German media caused the plant to close before it ever opened. After investing a reported $4 billion and nearly 19 years of effort into the project, the organizers finally gave up on it in 1991.

So what does one do with a completely useless, and almost completely built, nuclear power plant? You sell it. Dutch entrepreneur Hennie van der Most made claim for a relatively low $3 million. Known for his peculiar investments (he owns a chain of fried chicken restaurants and opened a golf course on a former NATO camp, for example), he was just the guy to turn the nuclear site into an amusement park, which opened in 1995.

The park is now part of a full-fledged resort called Wunderland Kalkar that also features a hotel, restaurants, and a heliport. The park itself contains over 40 attractions. Among them: a flying elephant ride and a spinning teacup attraction, just like the ones at Disneyland.

But the plant’s old cooling tower is certainly the park’s biggest and most singular draw. The exterior, which is now covered in a large mural of a mountain range, serves as a climbing wall. Inside, the tower houses a spinning ride called the Vertical Swing that protrudes over its topmost edge.

Amazingly, Wunderland Kalkar attracts over 600,000 visitors annually.