Kayamori Onsen Rotenburo

A riverside wild bath in the Yubara hot spring area of Okayama, unusual even by wild-bath standards, it sits directly in a riverbed and holds seven or eight people comfortably. The water runs at around 35°C, so more of a long warm soak than a hot plunge. It has historically been maintained by and for local residents, and outsider access has become restricted due to past etiquette issues.