Sarutobi-Sentsubo Gorge is located in the course of Yamakuni River running through Yamakuni-machi-Kusamoto in Nakatsu City, Oita Pref. The name “sarutobi (flying monkey) comes from wild monkeys once jumping over the valley. Nearly 70% of the whole area of Yamakuni Town lies on the highland with a height of 300-700 m. This town with a population of no more than 3,500 has been known for its beautiful mountains and forests as a part of Oku-Yabakei since the ancient times. At the bottom of the river several pit holes have been made by pebbles rolling among rocks in the riverbed for a long time. The pit holes, the largest of which is 1 m in diameter and 2 m in depth, can be found in the area covering as long as 2 km. The group of pit hole is nationally designated as Natural Treasure. Sarutobi-Sentsubo Gorge in Oku-Yabakei is certainly a scenic beauty composed of strange-shaped rocks and clear stream of water.