A grotto is a stone chamber with Buddha statues carved into a mountain wall. This type of Buddhism architecture originated in India and was imitated in China’s earliest grotto designs. China’s grottoes were built in the Yellow River Basin. The peak period of grotto construction was from the Northern Wei Dynasty to the Sui and Tang Dynasties. The Dunhuang Mogao Grotto and Tianshui Maijishan Grotto in Gansu Province, Datong Yungang Grotto in Shanxi Province and Luoyang Longmen Grotto in Henan Province have been appraised as China’s four main grottoes. China’s grottoes share similar geological characteristics with those in other countries: (1) All grottoes were carved in rocks with hardnesses below 5 on the Mohs scale. (2) All grottoes are located on isolated mounds. (3) The grotto niches are generally not more than 200 m above the local ground level. (4) Grottoes are generally built on steep cliff walls facing a river.