The Vredefort Dome was declared a world heritage site in 2005, this is the seventh site in South Africa.
The reason for this declaration is that it is the largest and oldest meteorite impact structure on earth.
About 2 billion years age, near the small town of Vredefort, some 120 km south west of Johannesburg an enormous meteorite measuring 10 - 15 km in diameter smashed into the earth. This resulted in an enormous crater 200 - 300km in diameter at the center of the crater was a prominent uplift, like the splash when a stone is dropped into water. This uplifted area measuring 100 km across bringing some of the oldest rock on earth to surface.
The United Nations Educational , Scientific and cultural Organization (UNESCO) described the Vredefort Dome as "the Worlds Greatest Known single energy release event"
"Vredefort Dome" by David Fleminger, South Bound Pocket guides to South Africa's world heritage sites.