Koganeyu, in Tokyo's Sumida ward, is the bathhouse most frequently cited in coverage of Japan's design-sento boom: a 1932 neighborhood sento (public bath) that closed for a full renovation in 2020 and reopened with a proper sauna, a craft-beer taproom that doubles as a DJ booth, and international design-press coverage most bathhouses never get. On July 7, 2026, it opened a second location in Shinjuku. For anyone reading this as a market rather than one good renovation, that second opening is the more interesting fact: the format is starting to repeat.
A sento is licensed, and the license caps the price of the core product. What Koganeyu has now shown twice is where the money to rebuild around that cap can come from.
What the price ceiling covers
Each prefecture sets a maximum charge for the standard adult bath at a facility licensed in the general public bath category, and operators near that ceiling do not compete on price. That is a narrower rule than it sounds: it covers the basic tub. Anything beyond it — a sauna, a cold plunge, a rest area, a timed premium session — is priced freely, even inside a fully licensed house. A separate registration category also exists for bathhouses operating outside the general classification; those set their own price for the basic bath as well as the extras. Which category a renovated house sits in is an uneven story across the industry, and one this journal's paid Japanese-language market notes track in more depth than a launch piece can.
The rule has kept the basic bath within reach of ordinary households for generations. It has also meant the number of licensed sento nationwide has been shrinking for decades, as retiring owners find no buyer willing to run a business whose core product cannot be repriced.
In Tokyo and the wider Kanto region, the building type that grew up under this rule is distinctive: a tiled mural of Mount Fuji over the bathing hall, a tall chimney marking the house from the street, a high-ceilinged changing room. Kansai never developed the same mural tradition, so what follows describes a Kanto style, not a national one.
One renovation, then a format
Koganeyu's original Sumida building, operating since 1932, reopened in 2020 after a renovation by Schemata Architects under Jo Nagasaka, who kept the two bathing pools at their original footprint and turned the unused boiler room, storage, and machine room into functions the license doesn't touch. A new Mount Fuji piece by illustrator Yoriko Hoshi — a contemporary picture-scroll rendered in mortar and ink — spans the width of both bathing halls as a single narrative: the traditional mural reinterpreted rather than reproduced, inside a building otherwise rebuilt around it.
The Shinjuku location, opened this month, is a different building with the same instincts applied to it: a longstanding neighborhood bathhouse, formerly the Kanazawa Bathhouse, converted rather than replaced. Interior design comes from a different architect, Yuko Nagayama, while branding continuity comes from artist Hiroko Takahashi, who also shaped the original Sumida identity. The sauna area alone runs two distinct rooms, one per changing side, plus microbubble cold water drawn from groundwater — a more ambitious build than the first location's.
That is the detail worth sitting with. One well-documented renovation is a case study. A second location, under a different architect but the same name, the same branding hand, and the same sauna-plus-beer-plus-design formula, is a format — evidence that design-sento economics can now be deployed onto an existing building rather than reinvented for each one.
Where the architect's fee comes from
Here is where I want to be careful about what the evidence actually supports: neither location publishes a facility-level financial split, and I have not seen either set of books. My reading, not an audited fact, is that a separately priced sauna is the kind of revenue that could plausibly fund renovations at Koganeyu's scale, twice over, because it is the one part of the operation exempt from the price ceiling. What is verifiable is the structure that makes that reading plausible: the bath is capped, the sauna is not.
Both locations follow the pattern covered in The Boom That Rebuilt the Japanese Sauna: löyly — water meeting the stove's hot stones — is built into the rooms rather than bolted on. Shinjuku implements it both ways at once: in the women's THE COCOON, guests ladle the water themselves; in the men's THE ABYSS, automated pours run on a cycle. And the rooms are sized to hold a group through a full heat session rather than a handful of solo bathers. None of that touches the regulated bath's price. All of it sits on the free side of the ledger, the side that can fund an architecture commission, and now a second one.
What one brand doesn't prove
This is a read on one operator with two buildings, both in Tokyo, not a survey of Japan's remaining licensed sento. Whether other renovated houses are moving toward a repeatable format, or Koganeyu is simply first to manage it, is more than two data points can settle. Full facility counts, and the pricing-category breakdown behind them, are what the author's ongoing market analysis, published on note, exists to establish properly.
Visit both locations if you can compare them. Sumida is the original, the room the architecture press already knows. Shinjuku is the test of whether the formula travels. Each is honest about which part of the building is paying for the other.
If you want either 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.