Numajiri Motoyu Yubatake

One of Japan's great wild hot springs, the source of the Numajiri hot-spring area sits at around 1,300 meters on the flank of Adatara, where a powerful sulfur spring (one of the highest single-source flow rates in Japan) cuts through rocky gorges. The water is intensely acidic and runs near 70°C at the source, cooling to bathable temperatures in natural pools further downstream. Getting there takes about 30 minutes on foot along a trail past a white waterfall and cave sections; the sulfur smell hits you before you arrive. Beautiful, genuinely wild, and not without risk, hydrogen sulfide concentrations can be high, so stay alert.