Ultimate Style: Bringing Resort Spa Living to an Apartment in Yamanashi, Japan

Some projects begin with a floor plan. This one began with a question: what does it feel like to come home to a hot spring?

The apartment sits on the fourth floor of a twelve-storey building in Yamanashi Prefecture, in the resort town of Ishiwa Onsen — about 100 kilometers, or an hour and twenty minutes by car, from Tokyo. Mount Fuji is visible from the windows. The building itself sits on a natural hot spring, with a communal onsen bath occupying the 8th and 9th floors. The air outside is mountain-clean. Everything about the setting says escape.

Unwinding in the spa apartment, soaking in the view of Mount Fuji.

This project was completed in 2007, well before wellness-centered design or in-home chroma therapy had entered the mainstream vocabulary.

My clients were selling the idea of a second home to Tokyo residents in their 40s and beyond — people with the means to want a resort villa, but not the time or land to build one from scratch. This wasn’t a house. It was a single apartment unit inside a larger residential building: 64 square meters, second-hand, stripped back to bare shell. Small, by any standard. So the real design problem wasn’t decoration. It was how to make one compact unit feel like an entire private retreat.

Starting From the Bath, Not the Floor Plan

Most apartments are planned room by room — bedroom here, bathroom there, kitchen wherever it fits. I did the opposite here. Once I understood that this building sat above natural spa water, and that a communal onsen occupied two entire floors above us, it became clear that the bathing experience shouldn’t be a footnote inside this apartment. It should be the center of it.

The bathtub serves as the anchor, with the living, dining, and kitchen spaces arranged around it in an open-plan layout. This seamless design unifies the social heart of the home—cooking, eating, relaxing, and bathing—into one continuous, flowing gesture rather than a series of divided rooms.

So I removed every existing partition wall. Working from an essentially blank shell gave me the freedom to plan the whole apartment around a single fixture: a KOHLER Chromatherapy bathtub, positioned not in a closed bathroom but directly within the living space.

Click here to watch the Before & After video

The tub — from KOHLER’s Sok line, deep enough for full immersion, with a continuous overflow edge and integrated color-changing LED lighting — sits on a raised marble platform between the living/dining zone and a glass-enclosed shower wall finished in a shimmering copper-gold mosaic, also sourced from China. At night, the water glows: blue, violet, whatever mood you set with the remote. It isn’t hidden behind a door. It’s part of the room, visible from the sofa, from the dining table, from the kitchen island. The bath became the anchor everything else was arranged around, and the kitchen was aligned directly alongside it, open-plan, so the whole social heart of the home — cooking, eating, relaxing, bathing — reads as one continuous gesture rather than a sequence of separate rooms.

A glass-enclosed spa corner with triple rainforest showerheads set into the ceiling above the Kohler SOK tub, the bronze mosaic wall catching light from every angle. Sleek chrome fixtures, a tinted glass partition, and a warm marble surround complete this serene, spa resort-inspired bathing space.

Getting that tub into the apartment is its own small story. The Sok is a KOHLER product imported from the US, and when my client first tried to order it in Japan, he was told the wait would be six months. Instead, he flew to Shanghai, walked into a Kohler showroom, and walked out having bought the tub in forty-five minutes. China speed, as he put it.

Materials That Do the Work of Space

In an apartment this size, materials have to perform double duty: they need to read as luxurious without visually shrinking the room. I turned to Italian Calacatta Gold marble for the floors and bathroom walls, sourced through Shenzhen, China, where suitable stock was readily available and the price was significantly better than buying directly in Japan. The stone has a soft, luminous quality that avoids the heavier, darker character of many contemporary “luxury” surfaces. Light bounces off it rather than being absorbed, which does a lot of quiet work in making a small footprint feel larger than it is.

Texture in harmony—combining metallic bronze mosaics, dark wood paneling, rugged limestone, and refined Calacatta marble for a balanced, worldly aesthetic.

There was, however, one issue with the marble. When the Italian Calacatta Gold arrived on site, the client’s contractor had marked the front face of the slabs with a permanent red marker. The ink had penetrated the stone. Replacing the marble would have affected the schedule, while aggressive sanding could have damaged the polished surface. They therefore brought in a specialist stone restoration company from Tokyo. After several days of careful treatment, they were able to remove the marks without damaging the finish. The experience was a useful reminder that even small details in material handling can have significant consequences.

Against that pale stone, I introduced texture and warmth through a stacked limestone mosaic feature wall, sourced from China, the kind of surface that catches concealed lighting and throws soft shadow across its irregular coursing, giving the living and bedroom areas a tactile, almost geological presence. It’s the material equivalent of stepping outside: rough, natural, sun-warmed.

For contrast and structure, a pair of dark teak louvered screens stand like sentinels flanking the entry to the living space — geometric, almost architectural in their own right, black against the warm stone. They act as a soft room divider without ever fully closing the space off, letting light and sightlines pass through their slats while still giving definition to where one zone ends and another begins.

In the bathroom, glass vessel sinks in a translucent sea-glass green by HUA and faucets by DAMIXA (both from Denmark), also sourced from China, sit on a floating marble vanity beneath backlit mirror panels — small, deliberate departures from an otherwise neutral palette that keep the room from feeling monochrome.

Sleek and modern: Green glass vessel sinks by HUA paired with DAMIXA Denmark faucets, resting on a floating Calacatta Gold marble vanity in the spa apartment’s bathroom.

Light as a Material

Almost none of the lighting in this apartment is visible as a fixture. The living room runs almost entirely on concealed light — recessed into a soft ceiling recess that washes the space in an even, shadowless glow, more like daylight through a scrim than a bulb in a socket. Behind the limestone feature wall, additional hidden lighting grazes the stone’s texture, catching every ridge and edge without a single visible source. Down lights handle the rest of the apartment. Even the bathroom mirrors are edge-lit, glowing as objects in their own right rather than merely reflecting light from somewhere else.

This was deliberate. In a small apartment, a visible light fixture is one more object competing for space in an already tight room. Concealed lighting removes the object and keeps only the light — which does far more to expand a room than any single lamp could.

Furniture as Punctuation

Against all that warm stone and soft light, the furniture needed to hold its own without adding visual weight. A black leather sofa on a chrome frame, a glass-and-chrome dining table, a glass coffee table with a slim black steel base — all sourced from China, all with a see-through or reflective quality, so that even fully furnished, the room never feels crowded. The one exception is a black-and-white swirl-pattern area rug, bold enough to anchor the seating area and give the eye somewhere to land amid all that pale marble and glass.

Living in the Kitchen

The kitchen — a Toyo Kitchen system from Japan — with its glossy black lacquer cabinetry under a white stone countertop, sits as an island between the dining area and the bathing platform, mirror-backed to double its apparent depth. Twin stainless steel range hoods — one for the kitchen, one visible in the mirror’s reflection — punctuate the ceiling line. It isn’t tucked away. It’s positioned so that whoever is cooking can see the tub glowing on one side and the dining table set on the other. Nobody in this apartment is ever more than a few steps from anyone else, which was exactly the point: resort living isn’t about having more rooms. It’s about the rooms you do have talking to each other.

The heart of the home: A Toyo Kitchen system with glossy black lacquer cabinetry, white stone countertop, and a mirrored wall, seamlessly integrated into the spa apartment’s open-plan layout.

The Point of All of This

I keep coming back to two ideas in my own work: less is more, and form follows function. Neither is original to me, but both mattered enormously here. There wasn’t room in 64 square meters for excess — every material, every fixture, every wall (or lack of one) had to justify its presence by making the space feel larger, calmer, or more connected to the landscape outside.

What this apartment proves, I think, is that a resort feeling isn’t a function of square meters. It’s a function of what you choose to remove, what you choose to let glow, and what you position at the center of a home instead of hiding it away. A hot spring inspired a bathtub. A bathtub reorganized an entire apartment. And an entire apartment, in the end, became the argument that healing and relaxation don’t need more space — they need better decisions about the space you have.

— Genco Berk