Recently nominated to UNESCO's World Heritage List.
From the UNESCO Advisory Body Evaluation:
The Vredefort Dome meteorite impact structure is the oldest (2023 million years) and largest (radius 190 km) so far found on earth...The impactor that formed the meteorite impact structure at the nominated property was either a large body such as an asteroid with a diameter of about 12 km traveling at a relative velocity of 20 km/sec, or a smaller one, such as the head of a comet, approaching at a much higher speed. The impact event created the greatest single energy release event known for the surface of the earth.
The meteorite impact structure was estimated to have been created in about 4 hours.