This mysterious cave ruin consists of two huge rocks, 24m and 15m high, supporting each other to form a cavern, with a perfect triangular rock of about 2m nestled in the gap between them. Due to its spectacular scenery and mystical nature, it has attracted attention as a power spot, and it is said to be the cavern of "Yamasachihiko" (aka "Hoori no Mikoto"), who spent his childhood by the Iwaiko River.