(From the Encyclopaedia Britannica.)
The Rubʿ al-Khali sand desert, covering about 250,000 square miles (650,000 square km) is the largest area of continuous sand in the world. The topography is varied. In the west the elevation is as high as 2,000 feet (610 m) and the sand is fine and soft, while in the east the elevation drops to 600 feet (183 m) with sand dunes, salt flats, and sand sheets. One of the driest regions in the world, it is virtually uninhabited and largely unexplored.