Around 40 mln people live in cave dwellings called yaodongs. I was very excited to finally be able to visit them, and after 3hours in train and 2h in buses we found one of the most curious yaodong villages in China. Now, on the fringes of Sanmenxia city we can find the underground village discovered in the 50s and then published in famous Architecture without Architects by Bernard Rudofsky.
Houses are created by sunked rectangular courtyards measuring ~ 8 x 6 m, from which separate arched rooms were dugged. The earth that surrounds the indoor space serves as an effective insulator keeping the inside of the structure warm in cold seasons and cool in hot seasons. Consequently, very little heating is required in winter, and in summer, it is as cool as an air-conditioned room. We visited the caves on a hot August day and the rooms stayed nice and cool.
Entrances to the dwellings were separated from the courtyard itself.