30 million Chinese still live in caves. LOL - really, the sheer level of absurdity of that country continues to startle.
30 million live in caves in China* - New York Daily News
Those are Yaodong, and it is part of culture and heritage around Loess Plateau in China's north. 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. So they are very energy efficient.