Descending along a gentle path alongside a beautiful mountain stream from the Small Hell, after about 15 minutes, you will reach a secluded place in the deep mountains adorned with towering trees, where the Issai-Kyō Waterfall is located. In the first year of the Taihō era (701), the Bodhisattva Gyōki, upon seeing the volcanic smoke of Mount Unzen from Amakusa, designated this place as a sacred site for the propagation of Buddhism. Crossing through Kuchinotsu and passing through Aruke, he arrived at the Issai-Kyō area of Mount Unzen and built a hall here, establishing it as a place for Buddhist practice.
The term 'Issai-Kyō' refers to all Buddhist scriptures, and it is said that Gyōki let the scriptures flow from this place. Downstream from here is also known as the 'Koyaba Valley,' continuing the breathtaking beauty of the ravine."