Koganeyu is a neighborhood sento (public bath) in Tokyo's Sumida ward, in business since 1932. In 2020 it closed for a full renovation and reopened with a sauna, a craft-beer taproom, and a DJ booth. The design press noticed, and kept citing it.
On July 7, 2026, Koganeyu opened a second bathhouse in Shinjuku. That changes the story. One renovation can be a one-off. A second building under the same name is a business model.
A bath with a price ceiling
A sento runs on a license, and the license fixes its price. Each prefecture sets a maximum charge for the standard adult bath; operators near the ceiling cannot raise it. The cap applies only to the basic tub, though. A sauna, a cold plunge, a timed premium session — all priced freely, even in a fully licensed house. (There is also a separate license category with no cap at all; which category a renovated bathhouse chooses varies across the industry.)
The ceiling has kept bathing affordable for generations. It has also been slowly killing the trade. Licensed sento have been closing for decades, because nobody wants to inherit a business whose core product cannot be repriced.
One renovation, then two
Schemata Architects, under Jo Nagasaka, handled the 2020 renovation. The two pools kept their original footprints. The dead space — boiler room, storage, machine room — became the sauna and the taproom, the parts of the house the price cap does not touch. Above the baths, illustrator Yoriko Hoshi painted a new Mount Fuji in mortar and ink, one continuous picture-scroll spanning both halls.
The Shinjuku bathhouse is a conversion of the former Kanazawa Bathhouse, another old neighborhood sento. The interior is by a different architect, Yuko Nagayama; the branding is again by artist Hiroko Takahashi, who shaped the Sumida identity. The build went further this time: two sauna rooms, one per changing side, and a microbubble cold plunge fed by groundwater.
Where the money comes from
Neither location publishes its finances, and I have not seen the books — so take this section as an operator's guess. The guess: separately priced sauna sessions are what made a renovation on this scale worth financing twice. The bath is capped. The sauna is not. That asymmetry is the engine of the design-sento model.
The saunas themselves follow the pattern this journal traced in The Boom That Rebuilt the Japanese Sauna: löyly — water on the stove's hot stones — designed into the room from the start. In THE COCOON, the women's sauna at Shinjuku, guests ladle the water themselves. In THE ABYSS, the men's side, automated pours run on a cycle. Both rooms are sized for a group to sit through a full session.
What two buildings prove
Two buildings, one operator, both in Tokyo. That is the extent of the evidence. Whether Japan's other renovated bathhouses are converging on the same model is a question for a survey, not a column — and the survey is what the author's Japanese-language market reports exist for.
If you visit, compare the two. Sumida shows where the model started; Shinjuku shows whether it travels. And if you would rather have the itinerary built for you, Japan Bathing Journal's Bespoke desk plans it.
— Takayama Sauna, Editor-in-Chief
Lead photograph: the bathing hall at Koganeyu Shinjuku, with the mosaic mural inherited from the former Kanazawa Bathhouse. Photo courtesy of Koganeyu Shinjuku, via PR TIMES.