In the rather grand plans for Berlin from Hitler, there was a central place for a 7 kilometer long north-south-axis, that ought to run from the Volkshalle (also known as Big Hall) to a victory arch that would dwarf the Arc de Triomphe in Paris.
To test whether the soil in Kreuzberg could cope with such an enormous construction, a large concrete rock was built as a test. This Schwerbelastungskörper started to sink in the ground several centimeters pretty quickly. Then came the end of the war, and the megalomaniac ideas of Hitler could be burnt.
But the Schwerbelastungskörper proved hard to destroy. That’s why it is still there as one of the most unknown tourist attractions of Berlin. In the weekends guided tours are sometimes available.