Abstract: In the recent two decades, the authors have investigated many large underground caverns in Zhejiang, Anhui and other places in China, including more than 3 000 ancient man-made rock caverns. Through field investigations, it is found that Tiantai Heidong underground rock caverns have the largest span of 92 m, Changyudongtian caverns have the maximum height of 99 m, as well as the most exquisite chisel imprints on sidewalls in Longyou Grottoes. These caverns have the same characteristics including excavated a few hundred years to several thousand years ago, have maintained the stability of thousands of years. These caverns have their own unique structures including inclined walls, fishtail-shaped pillars, inclined roof, dome, rib-shaped arch, thin common sidewall and horizontal partition between two caverns. Research results show that these unique structures play a crucial role in the long-term stability of the caverns. In addition, there are also many high-level technologies in the ancient large underground caverns such as the measurement technology, excavation technology and waterproof technology. These groups of unsupported large-span artificial caverns, which have been maintained for more than a thousand years, provide some enlightenments of the long-term strength, the water effect on surrounding rock and the evaluation of blasting damage. However, with the discovery of these caverns and the development of tourism, various kinds of deformations and failures have been produced, posing a serious threat to the stability and security of these ancient rock cavern relics. At the same time, some new topics and challenges have been proposed for the long-term protection of large-span artificial rock caverns.