More than 30 million Chinese citizens live in underground caves. Many peasants in the outskirts of cities like Yanan live in caves from the moment they are born until they become old enough and successful enough to move into the city to work. The caves are found all over the provinces of China and are usually one single, long room dug into the side of a mountain. The doors consist of rice paper or a colorful quilt. Apparently, they can be quite nice to live in.