The Wonder Cave, in Kromdraai, Gauteng, South Africa, is the third-largest cave chamber in the country, and is believed to be about 1.5 million years old. The single chamber has an area of 46000 square metres, and is 125 metres long and 154 metres wide.

It was discovered in the late 19th century by miners who dynamited and excavated limestone for the making of cement. Mining stopped during the Second Boer War, and never resumed.

The cave has about 14 stalactite and stalagmite formations up to 15 metres high, 85% of which are still growing. The 60 metre deep cave is accessible to visitors by elevator, and is located within the Rhino and Lion Nature Reserve, in the Cradle of Humankind, a World Heritage Site.

credited to wikipedia