Other forms: dunes
A dune is a natural hill made of sand, either on a beach or in a desert. It's a good idea to bring plenty of water and a camel if you're trekking across sand dunes in the Sahara.
Sometimes people drive special vehicles on the dunes beside the ocean — these are sometimes called "dune buggies." These seaside dunes are formed by a combination of wind and water, while the dunes in a desert are purely the result of wind. The origin of the word dune is somewhat uncertain, although it probably comes from a French word with an older Germanic root.