A huge underground project, which has been sleeping underground for thousands of years and is rare in the world, has been standing in front of historians, archaeologists, architects and tourists like a huge exclamation mark since it was accidentally discovered by several farmers 17 years ago. This is Longyou Grottoes, praised by tourists as "the most magical grottoes in the world". It is located in China and Zhejiang, with Liangzhu and Hemudu cultural sites. It has a long history and a rich collection of humanities. In the upper reaches of Qiantang River, at the intersection of Qujiang and Lingshan River, there is an obscure small county called Longyou. Although the county seat is small, its history can be traced back to the Spring and Autumn Period, when it was called "Gu Mi". It has been more than 2,500 years since then, and it is the second largest ancient capital in Zhejiang. Longyou Grottoes is located on a Linjiang hill 3 kilometers north of the county seat. Locals call this mountain "Copper tan shan". Fiona Fang is only a few miles away, but there are 24 artificial caves of different sizes and exquisite layout on the mountainside. Before they were discovered, they were all buried by submerged soil, and the rock mass at the mouth of the cave collapsed, making it difficult to see the real content. The local government has now developed five such caves for tourists to visit. These caves are roughly the same in shape and scale-the area of the cave hall ranges from hundreds of square meters to more than a thousand square meters; The height of caves ranges from 20 meters to 40 meters; The holes are all rectangular; The cave wall is steep, and the roof of the cave is inclined to extend in an arc; There are 2 to 5 thick stone pillars supporting the roof in the cave. Their cross sections are all made of iron, and the largest one needs 5 people to hold it. Without exception, the top of the cave, the wall of the cave and the surface of the stone pillar are all carved with fine twill, which looks like tiger spots; There is a wide stone step from the mouth of the cave to the bottom of the cave, which is a wave manifold; At the bottom of each cave, there are one or two excavated stone pools and artificial slopes.

A large number of experts and scholars have put forward various speculations and statements about the age and use of grottoes: quarries, tombs, Tibetan soldiers stations, ice depots, boulder culture, "Taoist paradise" and "rebel miners' refuge" and so on. Longyou Grottoes was once considered as an "abandoned quarry" at the beginning of this year, so it did not cause a sensation when it was discovered, and it was silent in Wenda for six years. It was not until 1998 that it attracted the attention of all walks of life. Today, similar grottoes are found all over the north bank of Qujiang, and there are at least 50 caves in the underground of 2.88 square kilometers nearby. Under the underdeveloped level of ancient science and technology, the completion of this huge underground project really makes people today incredible. Numerous mysteries in the grottoes make the audience "full of curious seekers when they enter the grottoes, and become riddlers when they leave the grottoes".

Among many researchers, Dr. Chu Cai Liang of Zhejiang University, after 10 many times of actual investigations and various historical data searches, proposed that Longyou Grottoes were first excavated in Xuandi of the Western Han Dynasty, and its function was to store grain, goods and war preparations. It was called "Beicangguan" in previous dynasties, especially in Sui Dynasty, and was listed as "historic site" at that time. Dr. Chu also found two convincing typical caves, one is a dustpan cave not far from the upper reaches of Tongtan Mountain (recorded in the Song Dynasty, called "eternal"), and the other is a stone cave not far from the lower reaches (there are three caves with waterproof stone dikes in front). But at present, at least it can be concluded that Longyou Grottoes are the largest ancient underground man-made buildings in the world. In addition, it also provides direct and powerful evidence for the "China's fifth greatest invention-drilling holes" proposed by foreign scholars.

The fog over Longyou Grottoes is gradually dispersing, and an ancient underground work of China with great cultural relics and archaeological value is being presented to the world. It is gratifying that Longyou Grottoes have been strictly protected by relevant parties and have been included in the agenda of applying for world cultural heritage. After all, Longyou Grottoes should also be a great witness of ancient human civilization.