Unzen Yokayu Public Spa

Yokayu is a day-use bath in Unzen, fed by its own source spring and kept flowing rather than recirculated. Unzen's onsen water rises from the jigoku (地獄), the steaming volcanic vents around town, and here it's a mild sulfur spring: soft on the skin despite the low pH, and reviewers describe it working gently into the body. Baths are split into men's and women's indoor and open-air sections, with six private family baths for those who want to soak alone. The building has kept a Showa-era feel, and the bathroom is reached by a stairway down to the basement. An annex next door offers simple self-catering rooms for longer stays in Unzen, though the rooms themselves have no bath, guests use the shared baths at Yokayu.