Yunpilbong Cave is a natural cave. The area mainly consists of micrographic granites of the Cretaceous period. There are many natural caves in Mudeungsan. However, the caves vary in shape and size depending on the origin of the rocks. The most widely known cave is found at Yunpilbong Peak (400 m above sea level), located to the east of Wonhyo valley. The natural cave here is called Anyang Cave. The cave is 3.7 m high, 13 m wide, and 21.4 m long. The cave has high value as it is a large cave formed in granite. There are other types of caves such as limestone caves, lava caves, and erosional caves in Korea. However, it is very rare to see a large cave preserved in its natural condition.