Tswaing, meaning “place of salt” in the Setswana language, is an ancient impact crater outside the metropolis of Pretoria in South Africa’s Gauteng province. The Tswaing Crater formed some 220,000 years ago when a giant meteorite slammed into the Earth, creating a half-mile-wide crater and destroying all vegetation within a 25-mile radius.

Today, a blind salt lake lies at the bottom of the crater, and the area is surrounded by dense tree growth. This natural wonder is a feature in the region that even a fair amount of locals aren’t unaware of. Yet it is clear that early humans in the area knew of the crater site. Stone Age implements and pottery have been discovered at the crater rim, where deposits of salt were collected by these early inhabitants from the lake at the bottom of the hole.

In the early 20th century, salt and soda ash were mined commercially from the crater lake. The mining went on for nearly 50 years, lasting until the 1950s. The remains of these activities are still present as ruins around the crater. At the center of the crater lake, you can see the remains of several boreholes from the drilling that helped confirm the meteoric origin of the crater.

The Tswaing Crater now lies within a protected reserve, with several hiking trails leading up to the crater rim and down to the lake.