This valley was carved out of granite porphyry by the clear waters of the Iwaiko River, which originates in the mountains of Mount Okue. The vivid, pure water and huge rocks blend in harmony with the surrounding trees, creating a beautiful natural landscape.
In the summer, the area is bustling with people enjoying mountain stream fishing, playing in the river, and camping.
Mount Okue and the Iwaiko River Valley are a treasure trove of nature, home to primeval forests of fir, hemlock, and oak trees, rare plants such as the Japanese lily and golden moss bamboo (a natural monument), and even the Japanese serow (a special natural monument). In 2017, the naturally rich Sobo-Katamuki-Okue mountain range was registered as a UNESCO Ecopark.