The Sahara gets very little rain - sometimes less than 25 millimetres a year, less than a shower in most countries. During the day, temperatures can reach over 50°C, but at night the same sand can be surprisingly cold because there are no clouds to keep the heat in. Desert animals and plants have clever tricks for surviving these extremes.
Underneath the great dunes, the Sahara is not just sand - it is also ancient rock with fossils of sea creatures from when the whole region was covered by a shallow ocean millions of years ago. There are also hidden underground lakes of water called aquifers, drilled into by desert communities for drinking water.
Camel caravans have crossed the Sahara for thousands of years, carrying salt, cloth and gold between cities. Camels can go without water for up to two weeks and store energy in their humps (it is fat, not water, inside the hump). Today, lorries carry most goods, but camel caravans still travel some of the old salt routes in Mali.