Blyde River Canyon
http://en.wikipedia.org/wiki/Blyde_River_Canyon
While it is difficult to compare canyons world-wide, Blyde River Canyon is one of the largest canyons on Earth, and it may be the largest 'green canyon' due to its lush subtropical foliage. It has some of the deepest precipitous cliffs of any canyon on the planet. It is the second largest canyon in Africa, after the Fish River Canyon, and is known as one of the great wonders of nature on the continent.
Possibly the best view in the whole of the Blyde River Canyon is of the "Three Rondavels", huge, round rocks, thought to be reminiscent of the houses or huts of the indigenous people, known as rondavels. This canyon is part of the Panorama route. This route starts at the town Graskop and includes God's Window, the Pinnacle and Bourke's Luck Potholes.