Sudwala Caves

The Sudwala Caves in Mpumalanga, South Africa, are set in Precambrian dolomite rock, which was first laid down about 2.8 billion years ago. The caves themselves formed about 240 million years ago. They are one of the oldest caves in the world. There are a number of speleothem structures in the cave, known by names such as the "Lowveld Rocket", "Samson's Pillar", and the "Screaming Monster"; some have been dated to 200 million years old. There are also microbial fossils of a cyanobacterium known as collenia in the rock; these formed 2 billion years ago. The caves were used for shelter in prehistoric times, probably due in part to a constant supply of fresh air from an unknown source in the caves.

Cave data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).