The world's largest sand dunes in terms of square miles are the Simpson Dunes in Australia. They cover more than 65,000 square miles of land area. The tallest roving sand dunes are found in the Namib Desert in Namibia, where a dune exceeds 1,200 feet.
The tallest stationary dunes are found in Mongolia, and they are over 1,600 feet tall. They also emit a constant hum that experts, to date, have not yet completely been able to explain. The tallest sand dunes in the United States are found in Great Sand Dune National Park in Colorado. There, visitors can scale dunes as high as 700 feet.