Simon Reeve travels across the Kalahari in southern Africa. Covering half a million square miles of desert and scrubland, it's one of the last great unspoiled African wildernesses, sitting on top of a vast basin of sand that in places reaches up to a mile in depth.Simon tracks wildebeest with a group of one of the region's indigenous inhabitants, the San, who are renowned for their hunting and tracking techniques. And he visits the Okavango Delta, which is transformed each year by seasonal rains from a desert to an oasis of greenery.