Cango caves are arguably the most impressive caves in Africa (or at least the guide said they were). The caves consist of a series of huge caverns filled with stalactites, stalagmites, pillars, and shapes that look like something from the mind of Geiger or Dali.
I did a guided "adventure tour" that went quite deep into the cave and required a fair amount of climbing and squeezing through tiny holes to get to places. Reportedly they had an incident a few years ago when a 300lb lady refused to listen to advice that she was too large to get through, threatened to sue unless she was allowed in, and then got stuck in one of the passageways, trapping not only herself but also the eight people on the other side of the passage for 11hours.
The San people used to shelter in the outermost cavern when it rained, but never ventured any further because they had no source of light and believed the caves were inhabited by evil spirits. They did however leave a nice set of cave paintings behind. Most of the cave network was discovered by a settler who explored the caves with an oil lamp and ropes. One cavern was discovered after the floor collapsed below a group of explorers, revealing that the flat floor they had been standing on was an inch-thick rock-sheet formed by limestone collecting on top of a now-gone layer of ice inside a larger cavern.
There isn't really much more to say. Just look at the pictures.