The Sudwala Caves in Mpumalanga, South Africa, are set in Precambrian dolomite rock, which was first laid down about 3800 million years ago, when Africa was still part of Gondwanaland. The caves themselves formed about 240 million years ago, making them the oldest known caves in the world.
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. In more modern times, the caves were discovered by Somquba, one of the sons of the Swazi king Sobhuza I, who was fleeing from his brother Mswati II. Somquba and his followers used the caves as refuge, until Somquba was killed in an unexpected attack. Survivors stayed on under the leadership of an inDuna (headman or leader) named Sudwala, thus the name.
During the Second Boer War, in 1900, the caves were used by the Boers to store ammunition for their 94-pounder Long Tom guns. It was thought that the caves may have been used by President Paul Kruger to store the legendary "Kruger Millions", gold bullion which reputedly disappeared somewhere between Waterval Onder and Nelspruit during Paul Kruger's flight from Pretoria to Lourenço Marques (now Maputo).
In 1914 a company was formed to excavate huge amounts of bat guano; this was sold as fertilizer to farmers.
The Sudwalaskraal farm that is home to the caves was purchased in 1965 by Philippus Rudolf Owen, and he opened the caves as a tourist attraction.
The major chamber in the Sudwala Caves is the P. R. Owen Hall; it is 70 metres in diameter and 37 metres high, with a constant temperature of 17°C. This chamber was used as a concert hall on a number of occasions, including July 1970, when the Russian singer Ivan Rebroff gave a concert. Concerts were stopped due to vandalism in the caves in 2002, but were started again in 2006.
There are a number of calcium 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 2000 million years ago.
The Sudwala Caves are a popular tourist attraction in Mpumalanga, and are next to the P R Owen Dinosaur Park. One-hour tours of the cave are run during the day, and a monthly five-hour-long "Crystal Tour" takes adventurous visitors 2000 metres through the cave, with the tour culminating at a crystal chamber that bears aragonite crystals.