Sarutobi potholes, Natural monument in Nakatsu, Japan.
Sarutobi Potholes comprise a series of round holes drilled into rock formations where the powerful Yamakuni River has continuously churned stones and water over centuries. The holes vary in size and sit across multiple exposed stone blocks in and around the riverbed, creating a natural sculpture carved by flowing water.
The site formed through natural erosion, a process that local people observed and documented long ago in regional records. It was later recognized as one of Japan's designated natural monuments due to its remarkable geological significance.
The name derives from mountain monkeys that once leaped across these rocks, connecting the site to local wildlife and traditional landscape use. Visitors can still see how the formations create natural pathways and stepping points across the riverbed, revealing the bond between the place and its animal inhabitants.
The site sits along the riverbed and is easy to access on foot, especially during months when water levels are lower and rocks are more exposed. Wearing sturdy shoes with good grip is important since the rounded rocks are slippery when wet or damp.
Each pothole displays different depths and interior textures, revealing how the river's strength and swirling patterns shifted over time at different locations. This variation tells the story of changing water dynamics and shows how each depression formed differently depending on the rock hardness and water pressure it faced.
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