Which desert has the highest sand dunes in the world?

Namib is a cool coastal desert extending for 1,200 miles (1,900 km) along the Atlantic coast of Africa from Namibe (formerly Moçâmedes) in Angola southward across Namibia to the Olifants River in the Western Cape province of South Africa.

The dunes run in lines from north-northwest to south-southeast, individual dunes having lengths of 10 to 20 miles (16 to 32 km) and reaching heights of 200 to 800 feet (60 to 240 metres). The troughs between these lines of dunes are interrupted by smaller transverse dunes.

The highest sand dune in the world, Dune 7, the 1,256-foot (382m) dune got its name because it is the seventh dune past the Tsauchab River, which runs through part of the Namib Desert. The desert itself, believed to be dry for at least 55 million years, is considered the oldest in the world.

The desert dunes are formed by the transportation of materials thousands of kilometres from the hinterland, that are carried by river, ocean current and wind. It features gravel plains, coastal flats, rocky hills, inselbergs within the sand sea, a coastal lagoon and ephemeral rivers, resulting in a landscape of exceptional beauty.