Shimosuwa Onsen, near Shimosha Akimiya Shrine, Shimosuwa, Nagano Prefecture
Koyu Bathhouse
A useful, inexpensive public bath near Akimiya for an early or late soak. Choose Tanga-no-Yu instead if you specifically want a very hot bath or an open-air pool.
Check before bathing
- Opening hours
- 05:30–22:00; last admission 21:30. Open daily, with occasional maintenance closures.
- Access
- A large car park has space for 45 vehicles. The rest room costs extra.
- Tattoo policy
- The facility's current first-party information does not confirm a tattoo policy. Check with the bathhouse before visiting.
Spring & water temperature
- Spring-source temperature
- Not published.
- Bathing temperature
- Not published.
- Spring source
- Shimosuwa Onsen water that includes the Wata-no-Yu spring system. Official pages confirm that Wata-no-Yu water reaches Koyu, but do not establish that it is the only source.
- Spring classification
- Natural hot spring; the current main official pages do not publish a facility-specific chemical classification.
- pH
- Not published.
- Flow rate
- Not published.
- Water handling
- Koyu is a public bath in the Shimosuwa Onsen supply network, and official sources confirm that it receives water from the Wata-no-Yu system. Current mixing proportions and bath-by-bath details for water addition, heating, circulation and disinfection are not published.
Bathing indications
The operator describes the water as gently warming. Local fertility stories are cultural traditions, not medical or pregnancy claims.
The current main official pages do not publish source-mixing ratios or bath-by-bath water-treatment conditions.
Admission is ¥300 for adults and ¥150 for children. The rest room is charged separately.
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.
