Sahara Desert

The world's largest desert aside from Antarctica, the Sahara is bounded in the North by the Atlas mountains and covers 8.6 million square kilometers - nearly all of North Africa. Despite the extreme temperatures (up to 136C in the daytime and well below freezing at night), parts of the desert are now surprisingly accessible and there is a burgeoning tourist industry. Being under the trade wind belt gives the Sahara a constantly changing face; its enormous sand seas and dunes ('Chgaga', the tallest, is over 500 meters high) are re-sculpted daily by sand-filled air currents such as the simoom and sirocco. The pristine nature of the Sahara means that unusual discoveries can be made, such as the 19-mile wide meteor crater discovered in Egypt in 2006. The impact of the meteor heated the surroundings to such an extent that it melted the sand, forming lime green glass, pieces of which can be found amongst the dunes. Twisted rock formations rear up from a desolate landscape of dry river valleys and steep gorges, and caves filled with carvings and paintings from before the desert was formed, such as the Cave of Swimmers, bear testament to the desert's watery beginnings. Just as it can reveal wonders, legend has it that the Sahara devours cities, explorers and whole armies, as in the story of King Cambyses of Persia, whose army of 10,000 men disappeared there 2,500 years ago and the remains of which explorers are still searching for.