Huan County belongs to the hinterland of the Loess Plateau, and the cave dwellings belong to the Longdong cave dwelling area of China's cave dwellings. It originated from the period when the ancient apes left their nests and "imitated the cave dwellings of animals". After millions of years of development and change, cave dwellings have become unique cave dwellings. The history of cave dwellings can be traced back to 4,000 years ago. 4,000 years ago, our ancestors used the special geological structure of loess to build houses, build cave villages, and develop agricultural and animal husbandry production. As early as the Xia and Shang dynasties, more than 10 generations of Zhou ancestors lived here. The earthen caves they dug and built are all over the mountains and valleys of the county, densely layered, and cave villages are lined up one after another. The "Book of Songs" calls it "Tao Fu Tao Cave", and it is recorded that the grandfather of King Wen of Zhou, Gu Gongfu, lived in a cave, which was the pioneer of the cave dwelling. Tao cave is a sunken pit manor; Fu cave is a semi-open manor on a slope. In the Western Han Dynasty, the shape and internal settings of cave dwellings were more suitable for people to live in. For example, chimneys and stoves were very particular, which were conducive to wind and smoke, and the cave dwellings were no longer polluted by smoke and dust. In the Tang and Song Dynasties, the types of cave dwellings increased. The functions of each cave dwelling were also divided. For a cave family, there were guest caves, kitchen caves, animal pen caves, and firewood caves. The cave dwellings were generally built in a sheltered and sunny place, avoiding moisture and staying dry, and avoiding shade and staying sunny, which made great progress and improvement in the cave dwellings. Since then, cave villages with hundreds of households and thousands of people have appeared in large numbers. In the Ming and Qing Dynasties, cave dwellings developed with safety, comfort and civilization as their goals, and tall walls surrounded a group of cave dwellings. There are as many as 150,000 cave dwellings in Huan County, accounting for 98% of residential houses. After the founding of New China, with the rapid development of the economy, the living conditions of farmers have been greatly improved, and many people began to move out of the cave dwellings and build brick and tile houses. However, nearly 95% of farmers in the county still live in cave dwellings and are obsessed with cave life. In recent years, although some farmers still live in the cave dwellings left by their ancestors, the appearance of the cave dwellings has also changed: first, the number of windows on the facade has increased, and glass has been installed to make the caves brighter and more light-filled; second, the outer circle of the cave mouth or the cliff face is lined with blue bricks to make the caves more solid; third, the walls and the kiln palms inside the caves are refreshed with white lime, and the ground is lined with bricks or floor tiles to prevent moisture and rats, clean and bright; fourth, some new high-end furniture such as televisions have been moved into the caves, adding a modern atmosphere to the quaint loess caves. The cave dwellings where farmers in Huan County live are basically earth cave dwellings, but a few brick hoop caves have appeared in recent years. Wherever they can dig a cave, they dig a large arched hole about 3 meters high, build a gable, open doors and windows, and build a kang against the gable inside the cave for people to live in. This is the cave dwelling room. This kind of cave dwelling saves labor and materials, and most farmers can afford to build it. The cave dwelling has high windows and doorways, which are convenient for air convection up and down. It can also be closed at any time to keep warm. It is warm in winter and cool in summer, and comfortable in all seasons. The ancients praised the cave dwellings here, saying: "Gentlemen from afar come to this village, don't laugh at the earthen cave without a house. Although it is not a fairyland, it is lovely to be warm in winter and cool in summer." There are many types of cave dwellings, including Fangmianzhuang and Luoquanzhuang. The cave dwellings include Mingzhuang cave dwellings, Dikengyuan cave dwellings and hoop cave dwellings. Mingzhuang cave: also called Yazhuang cave, including Fangmianzhuang and Liquanzhuang. It is generally located on the side of the mountain, the side of the ditch, and the city wall. It takes advantage of the cliff to first repair the cliff face, and then repair the village and dig the cave. The number of cave holes is based on the Yang number of the "Book of Changes". There are one village with three caves and five caves, and there are also more than five caves. This type of cave is the most common type of cave in Huanxian County. Dikengyuan cave: This type of cave is built on a large depression on a flat plateau. First, dig a rectangular pit on the flat ground, usually 5 to 8 meters deep, cut the four sides of the pit into cliff faces, and then dig caves on the four cliffs. And build a long slope lane or inclined hole on one side, leading directly to the original surface, as a sidewalk. This kind of cave is actually a basement, and the characteristics of "warm in winter and cool in summer" are more obvious, but due to the large consumption of manpower and financial resources, it is not common in Huanxian. Hoop kiln: Hoop kiln is generally made of adobe and wheat straw mud to form the base wall, and the kiln roof is arched. The filling soil on the kiln roof is double-slope, smoothed with wheat straw mud, and short rafters are pressed on the front and back. Some people also cover it with green tiles. It looks like a house from the outside, but a kiln from the inside. This type of cave is becoming more and more common. There are many types of caves according to their uses. For example, for anti-theft, a small kiln is built on the main kiln, which is called a high kiln; a small kiln that can hide things is built on one side of the kiln, which is called a crooked kiln; if the kiln is small, the kiln ribs are widened by four or five inches at the place where the kang is placed, which is called a kang kiln. The cave dwellings have different uses. The one in the middle is called the main cave or the guest cave, and the ones on the sides are called the side caves. There are also kitchen caves, sheep caves, cattle caves, firewood caves, grain caves, well caves, mill caves, and car caves.