The Sahara ("The Great Desert") is the world's largest hot desert and the world's second largest desert after Antarctica . At over 9,000,000 square kilometres (3,500,000 sq mi), it covers most parts of northern Africa; an area stretching from the Red Sea, including parts of the Mediterranean coasts, to the outskirts of the Atlantic Ocean. It is almost as large as the continental United States, and is larger than Australia. The Sahara has an intermittent history that may go back as much as 3 million years. Some of the sand dunes can reach 180 meters (600 feet) in height.