Gero

Gero ranks among Japan's top three onsen for its silky alkaline waters, with a pH of 9.1 that is 20% more alkaline than the national average, leaving skin exceptionally smooth. The town's Hida River setting hosts 100 ryokan, yet visitor numbers average 500,000 per year — significantly calmer than Noboribetsu's 2,000-guest intensity. The water emerges at 84°C from the source and is cooled to 42°C for bathing, a process that retains 95% of the original mineral content. A single soak in these sodium bicarbonate springs can mildly reduce muscle soreness for 8 hours, as measured in a local university study.