A dune is a hill or ridge of sand formed by wind. Picture a vast desert landscape where the wind constantly pushes loose sand into towering mounds, some as tall as skyscrapers. These sandy hills aren't permanent: the wind keeps reshaping them, slowly moving them across the desert like enormous waves frozen in slow motion.

Dunes form wherever there's plenty of loose sand and steady wind. You'll find them in deserts like the Sahara, but also along ocean beaches and even around the Great Lakes. Some dunes stay put when grasses and plants grow on them, holding the sand in place with their roots. Others, called wandering dunes or traveling dunes, migrate across the landscape year after year.

The shape of a dune reveals which way the wind blows. One side slopes gently where the wind pushes sand up, while the other side drops steeply where sand tumbles down. Walking up the gentle side feels like climbing a sandy staircase, but the steep side can be thrilling to run or roll down (though you'll end up with sand everywhere).

In literature and film, dunes often appear in desert adventures and science fiction stories, representing both beauty and harsh conditions where survival requires skill and determination.