Shuzenji-Okunoin is located upstream from the main hall in the Shuzenji Onsen area along the Shuzenji River (Katsura River), and is about 3 km further up after turning at the tributary Yubune River. It is said that young Kobo Daishi, the famous monk, studied here while traveling the country in pursuit of Buddhism. There is a legend that Kobo Daishi defeated the evil spirits by mantra. The area was filled with demons and evil spirits, so in order to prevent obstruction of his training, Kobo Daishi wrote sutras while facing the sky and sealed demons in a cave called Karigome-no-Iwaya. The wall around the cave creates a unique landscape by breaking the rock into thin plates. Such a structure is called platy joints and is thought to be formed when the lava cools. The rock exposed on the cliff is a lava flow from the Darumayama volcano and is made of dense andesite. Darumayama volcano is a large terrestrial volcano that was active about 500,000 to 800,000 years ago, and together with Osezaki and Ida volcanoes located in the northwest, it constitutes the Darumayama Volcano Group.