Rub' al Khali, Arabian Peninsula
The largest continuous sand desert in the world, the Rub' al Khali covers about a third of the Arabian Peninsula, an area that includes Saudi Arabia, Oman, Yemen and the United Arab Emirates. Understandably, it gets hot here. Hot, and dry. High temperatures have been recorded at 133 degrees, and there is no respite for the thirsty: Typical annual rainfall is less than 1.2 inches.
The Rub' al Khali is so inhospitable for humans that the desert had never been crossed unsupported and by foot until February 2013, when a South African team successfully traversed it.