Two thin timber decks hang in a cedar forest in Sagamihara, and not one tree came down to make room for them. The trunks pass through round holes cut in the boards and carry part of the structure as they go.
This is the Daichi Silent River Tree Sauna, the centerpiece of the Daichi Silent River retreat on the bank of the Dōshi River in Kanagawa, about an hour by car from central Tokyo. The retreat spreads guest cabins, a separate wood-fired sauna room and tent sites across a steep slope in the woods, each piece set apart from the next. Daichi runs the place as a campsite first, so the buildings sit inside a working forest rather than a landscaped resort. The tree sauna is the piece guests book first, and it’s the one the design world keeps circling back to. The site stayed whole.
The forest does the holding up
Daichi Inc designed the sauna around the trees instead of clearing them, so the forest works as structure and as the defining feature at once. The decks sit on timber grids, the grids rest partly on the trunks themselves, and the site’s natural slope carries the central platform from below. Each trunk gets a small circular cut-out in the deck boards, sized so the tree can keep growing through it season after season. The studio’s own project text calls the forest “an essential structural presence itself,” not scenery or background. Total floor area runs to just 100.4 square meters across both levels, which keeps the building light on the slope and smaller than the trees around it.
The trees stay alive inside the architecture, growing through it year after year. Nothing here is a backdrop.
Glass walls, a log burner, and the river below
Timber steps climb from the lower deck to the upper one, where the sauna room waits wrapped in frameless glass panels. Inside, a wooden bench runs along the glass and a single log burner stands at the center of the room, close enough to feed without standing up. The glass holds the view rather than the heat, so the forest stays in the room with you while the stove works. The heat comes from split wood, not a dial.
The rest of the upper deck stays open, edged with slender metal balustrades, and a small plunge pool sits out there for the pause between rounds. Below the decks, the Dōshi River does the same job on a bigger scale, and bathers use its water as the cold plunge. Sweating, cooling, climbing back into the heat: the loop runs through the forest instead of around it. The decks are left open and flexible on purpose, so a morning can drift from sauna rounds to lying in the shade without a schedule.
Inconvenience is the design brief
Daichi built the whole retreat on an unfashionable idea: inconvenience, designed on purpose. The shortcomings are deliberate.
The maker’s own description calls silent river a home for deliberate shortcomings, set there to wake the senses back up. Kindling a fire, boiling water, listening hard to the woods: the primal acts are the program, not a flaw in it. The tree sauna takes that brief furthest, hanging between the trunks as a space with no fixed job. In Daichi’s words, it “becomes a bed, a sauna, or simply a place to feel nature,” and inside and outside dissolve into one another while you sit there. Guests feel the boundary go soft, and that softness is the luxury on offer. Comfort comes second here.
Ninety minutes, six people, no staff in sight
The tree sauna books in 90-minute sessions, at 12:00 and 16:00 for day guests and at 7:00 and 19:00 for people staying overnight, and each session can be paired with the retreat’s separate sauna room. A session covers up to six adults, and the Tree Sauna site starts at ¥60,000, with full private hire at ¥70,000 for a day visit and ¥100,000 with a stay. Day sites elsewhere on the grounds start at ¥30,000, and stay sites start at ¥40,000.
The site works unstaffed, so nobody meets you at the gate. Rentals don’t exist here: the gear you need is the gear you bring up the slope. Bring a four-wheel-drive car for the entrance road.
The juries found it before the crowds did
In October, the FRAME Awards 2026 named the sauna Wellness Space of the Year in its hospitality judging, picked from more than 1,000 submissions by 100 jurors in Eindhoven. It also sits on the 2026 leisure and wellness shortlist at the Dezeen Awards, so the design world has marked the same small building twice in one season. The shortlist season is still running, with category winners due in November. Awards aside, the draw is simpler.
Who should make the drive
Go if a silent hour in the trees sounds better than a marble spa: the Tree Sauna site starts at ¥60,000 for up to six adults, so split it and the math turns friendly. Skip it if you want staff, towels and a locker room, because this retreat hands you none of those. The trees do the rest.