Shimabara, Nagasaki Prefecture
Hotel Seaside Shimabara High-Concentration Carbonated Spring
A rare natural carbonated spring paired with a sea-view bath, sauna and a separate Shimabara Onsen bath. The published carbon-dioxide concentration is unusually specific, but it does not mean every pool has the same concentration or temperature.
Check before bathing
- Opening hours
- Main-building bath 12:00–23:00, last admission 22:00. New-building view bath 06:00–12:00 and 15:00–23:00, last admission 22:00. Adults ¥800, children ¥400; towel ¥200. The facility and local tourism pages list ¥800; an older FAQ still shows ¥700.
- Access
- About a 10-minute walk from Shimabara Port; a large car park is available. The walk connects with the ferry from Kumamoto.
Spring & water temperature
- Spring-source temperature
- 26.0°C; this is the spring temperature, not a fixed bath temperature.
- Bathing temperature
- Not published.
- Spring source
- The hotel's natural high-concentration carbonated spring; a formal source name and well number are not published.
- Spring classification
- Carbon dioxide-bearing magnesium-calcium-sodium bicarbonate spring.
- pH
- Not published.
- Flow rate
- Not published.
- Water handling
- The operator confirms natural high-concentration carbonated spring water in both the main-building bathing area and the new-building view bath, alongside ordinary Shimabara Onsen. Mixing and treatment details by pool are not fully published.
The operator's measured 1,800–1,900 ppm carbon-dioxide range does not guarantee an identical concentration throughout every pool. Leave the bath if you feel dizzy, unwell or short of breath.
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.
