Some caves are primitive and simple ancient dwellings on the Loess Plateau, which are a portrayal of the cave life of our ancestors. There are many remains between the ravines on both sides of the Yellow River in Lanzhou. The biggest feature of caves is that they are warm in winter and cool in summer. There are roughly three kinds of caves in Lanzhou: earth kiln, hoop kiln and brick hoop kiln. Earth kilns are the most common. Choose a cliff with thick and hard soil. Dig out the cliff face first, and then dig out a large semi-circular cave. Finally, build a wall, install doors and windows, and set up a stove to support people. Some people collude with each other in the three-hole cave on the same facade to expand the use area, and some also dig a small kiln to store food or sundries. Earth kilns are low in cost and can be built as long as there is labor, so they used to be the first choice for poor people to build houses.