Sand dunes rippled in the Namib Desert of Namibia.

The Namib Desert, a coastal desert in south-western Africa, is a vast expanse of orange sand. The desert boasts some of the oldest (~55 million years) and highest (1,000 feet) sand dunes in the world.
The dunes, shown rippled in this image taken by an astronaut in orbit, receive extremely low rainfall each year, due to a cool ocean current, called the Benguela Current, that snakes up the coast from southern Africa. This cool current contributes to fog in the desert, which provides enough moisture for sparse vegetation to occupy some of the dunes.

Image credit: NASA/Johnson Space Center