Giant sand dunes are large hills of sand formed by the wind. They can be found in deserts and coastal areas, where loose sand accumulates over time. These dunes can reach impressive heights, sometimes exceeding 500 feet, and can change shape and size due to shifting winds. The formation of giant sand dunes involves processes like erosion and deposition. As the wind blows, it picks up sand particles and carries them until they settle in a new location. Famous examples of giant sand dunes include the Sossusvlei dunes in Namibia and the Great Sand Dunes National Park in Colorado.