Seiunsou or Kojigoku Onsenkan? Two Baths in Unzen Compared

Seiunsou and Kojigoku Onsenkan sit about a five-minute walk apart and both list the spring name as Unzen Onsen (Kojigoku). The choice is less about which name appears on the analysis sheet and more about the visit you want: Seiunsou is a ryokan bath with an outdoor pool, indoor baths and places to rest; Kojigoku is a modest wooden bathhouse focused on the milky sulphur water.

The usual adult price difference is ¥380. That buys a different setting, not a better grade of the same visit.

Kojigoku has had a one-off September 17–18, 2026 closure notice; those dates have passed. The usual Wednesday closing rule still applies, but future maintenance notices take priority. Check the current notice before travelling.

Go to Seiunsou for the outdoor bath and room to linger

Seiunsou suits a first visit when the surroundings are part of the point. Its public outdoor bath looks into the forest and sits near the sound of a stream; indoor baths, a rest area and a restaurant make it easier to spend a longer stretch there. The property describes its outdoor, indoor and private baths as free-flowing spring water.

Day use runs from 11 a.m. to 6 p.m.

A private bath is a separate purchase: the room costs ¥2,500 for 50 minutes, on top of admission. For two adults that comes to ¥4,260. Day visitors cannot reserve that private slot in advance; ask at the front desk on arrival. For a detailed breakdown, see the Seiunsou private-bath guide.

The extra facilities matter most if you plan to use them. If you only want one short soak and will leave, paying more for the ryokan setting may not add much.

Kojigoku is a simpler stop centred on the bath itself

Kojigoku Onsenkan is the more focused visit: a gender-separated indoor bath in a wooden building, with cloudy water and a sulphur scent. The bathhouse opened as a communal facility in 1919; the current building dates to 1993. It has no outdoor pool, private room or sauna. There is a rest space, but this is not a hotel-style spa.

Its lower price and earlier opening time make it useful for a morning soak. The operator lists hours of 9:30 a.m.–7 p.m. and Wednesday closure, with Wednesday public holidays open. It does not publish a last-entry time, so do not leave arrival until the last few minutes.

Amenities are sold separately; bring a towel and wash items if you prefer not to buy them there. The Kojigoku Onsenkan guide covers the walk, water information and current limits in more detail.

The same spring label does not make the baths interchangeable

Both facilities’ current spring information uses the name Unzen Onsen (Kojigoku), and the latest analysis lists a source temperature of 51.1°C. That is a source reading, not the temperature of either bathing pool. Seiunsou publishes more detail about how it supplies its baths, including use of local spring water to cool the water before it reaches a tub when necessary.

Kojigoku describes its water as flowing directly into its communal bath. Neither figure proves that the water feels identical in every pool or on every visit.

You can visit both, if the day has room

Because the walk between them is short, visiting both can make sense for someone who wants to compare a ryokan-style outdoor bath with a traditional indoor communal bath. One option is to start at Kojigoku after its 9:30 opening, then return to Seiunsou after 11. Alternatively, arrive at Seiunsou for the outdoor bath and walk up to Kojigoku later. Adult admission for both is ¥1,380, before towels, food or transport.

Do not schedule the second soak simply to “get your money’s worth.” Both are sulphur baths; take a break, drink water and keep each soak comfortable. If you are travelling by bus, check the uphill and return services first. A 7 p.m. closing time is not evidence that a useful bus leaves afterwards. The nearest stop is Kojigoku-iriguchi; Seiunsou lists local transfers as an option to ask about, not a guaranteed shuttle for every day visitor.

The nearest stop is Kojigoku-iriguchi. Check the uphill route and return timetable before bathing; the 7 p.m. closing time may be later than the last useful bus. Seiunsou offers local transfers by request, not a regular day-use shuttle.

Ask each operator about tattoo access. Their public information does not establish one shared rule for both baths.

Which one should you choose?

Pick Seiunsou for the outdoor setting, a longer visit, or access to more facilities. Pick Kojigoku when the bath itself is enough, you want to spend less, or you are arriving before Seiunsou’s day-use window begins. If the main requirement is bathing in the same room as a partner or child, neither regular public bath is the answer; compare Yokayu’s family baths instead.

Sources

- [Seiunsou day-use bathing](https://www.seiunso.jp/oneday/) - [Seiunsou spring information](https://www.seiunso.jp/spa/) - [Kojigoku Onsenkan official page](https://www.seiunso.jp/kojigoku/) - [Kojigoku Onsenkan 2026 spring analysis (PDF)](https://www.seiunso.jp/wp-content/uploads/2026/03/analysis202602-1.pdf) - [Seiunsou access information](https://www.seiunso.jp/access/) - [Seiunsou current notices](https://www.seiunso.jp/): one-off Kojigoku closure notice for September 17–18, 2026 (dates now passed). - [Unzen day-use bath guide](/guides/unzen-day-onsen-guide/)

Checked September 28, 2026. Hours, prices and temporary closures can change; check both operators’ latest notices before setting out.