Along the way, the landscape changes completely. At the bottom you might be walking through warm green farmland and banana trees. As you climb higher, the plants get smaller. Higher again, the trees disappear and the land is rocky and quiet. At the very highest point - Thorong La pass at 5,416 metres - there is only snow, sky and wind.
You sleep in 'tea-houses' - small mountain inns run by local families. They cook for you, give you a bed, and often share stories about their village. Children from the village often come and say hello to the walkers, and walkers sometimes share photos of their own home in return.
Because of altitude, you have to walk slowly and rest often. The body needs time to get used to less oxygen. Local guides tell walkers a saying: 'go up high, sleep down low.' It means: climb a little higher each day, then come back down a bit to sleep - that's how the body learns.
The reward is the view. From the high points of the Annapurna Circuit, you can see seven of the highest mountains in the world all at once - a wall of white peaks above the clouds.