Unzen, Nagasaki Prefecture
Kojigoku Onsen Hall
A compact communal bath for milky sulfur water, reached by a short uphill walk from Seiunso. Its weekly Wednesday closure and the spring's acidity are worth factoring into the visit.
Check before bathing
- Opening hours
- 09:30–19:00 year-round from April 2026. Closed Wednesdays unless Wednesday is a Japanese public holiday. Adults ¥500; ages four through elementary school ¥250; children under four enter free. Bathing supplies cost extra.
- Access
- About a 5-minute uphill walk from Unzen Seiunso, near the Kojigoku Iriguchi area.
- Tattoo policy
- A 2018 national tourism document listed Kojigoku among communal baths without tattoo restrictions, but the current facility page does not restate a rule. Confirm before making a special trip.
Spring & water temperature
- Spring-source temperature
- 51.1°C in an on-site source survey on 2026-01-30; the air temperature during the survey was 3.1°C.
- Bathing temperature
- Not published.
- Spring source
- Unzen Onsen, Kojigoku source area.
- Spring classification
- Simple sulfur spring, hydrogen-sulfide type; low-salinity, weakly acidic and hot spring.
- pH
- 4.41
- Flow rate
- Not published; the 2026 analysis sheet leaves the flow-rate field blank.
- Water handling
- The operator describes milky sulfur water flowing directly from the source into the bath. Current published material does not fully specify added water, heating, circulation, filtration or disinfection by pool.
- Analysis date
- 2026
This is a weakly acidic sulfur spring. Avoid bathing after drinking, hydrate before and after, and seek medical advice if you have sensitive skin or mucous membranes, a chronic condition or feel unwell.
How to read a bath profile
Spring-source temperature and actual bathing temperature are kept separate. Each score is shown independently for comparison rather than collapsed into one overall score.
