Table of Contents

• Yashima-ru (Kagawa) | A Corridor Observatory Overlooking the Seto Inland Sea
• Senkoji Summit Observatory PEAK (Hiroshima) | A Viewpoint in Harmony with the Town and Sea
• Kirosan Observatory (Ehime) | Kengo Kuma’s “Invisible Architecture”
• Sasayama Castle Oshoin (Hyogo) | A Monument of Samurai Culture and Architectural Renewal
• WEEK Kamiyama (Tokushima) | A Creative Retreat Breathing Life into the Mountains
• A Journey of Coexistence Between Nature, People, and Architecture

Yashima-ru (Kagawa) | A Corridor Observatory Overlooking the Seto Inland Sea

High above Takamatsu, Yashima-ru stretches along the edge of the plateau like a glass horizon line, its roof tracing the curve of Mount Yashima. From inside, the city unfolds below in clean grids and harbors, ferries and fishing boats drawing slow white lines across the Seto Inland Sea. On clearer days, layered silhouettes of islands appear across the water; on hazier ones, a faint mist softens their outlines so that sea and sky seem to fade into each other at the edge of the windows.

The building itself was born from an earlier observation deck, opened in 2022 with a clear brief: to avoid blocking the view and to merge quietly with the mountain. A 200-meter corridor follows the natural slope, encouraging visitors to walk along the curve rather than stand at a single point. Locally quarried Aji stone is used for the roof tiles, tying the structure to the geology of the region; from a distance, the roof reads almost as an extension of the plateau.

Inside, “One Night’s Dream in Yashima,” Japan’s only panorama museum, is a continuous, five-meter-high, forty-meter-long oil painting that wraps around the room. Viewed together under carefully controlled lighting, the boundary between history and art almost disappears, and scenes inspired by the Genpei War begin to read like a dream unfolding around the visitors. Before entering, guests wait in darkness to let their eyes adjust, then step into a space where the story progresses from morning to midday to night, accompanied by music and an audio guide that reinforces that sense of moving through a single, continuous day.

At night and during seasonal events, Yashima-ru shifts from a quiet observatory to a stage. Live performances and summer fireworks turn the terrace into a gathering place, with reserved seating inside the glass corridors for those who plan ahead. On a permanent basis, there is a cafe and a merchandise shop, convenient for a relaxing stop. In daylight or after dark, the architecture functions less as an object and more as a frame, drawing attention back to the water, the islands, and the city that first shaped its design.

Senkoji Summit Observatory PEAK (Hiroshima) | A Viewpoint in Harmony with the Town and Sea

Renewed and reopened in 2022 at the summit of Mt. Senkoji, Senkoji Summit Observatory PEAK feels like a natural continuation of the town’s climbs and switchbacks. Many visitors still reach it on foot, following the route that threads from Cat Alley up through temple precincts and the literary path before emerging at the parking area near the top. Others choose the ropeway from the shopping arcade or arrive by taxi, reaching a parking area near the summit. In every case, the approach matters: the observatory is designed to be experienced in motion, as another stage in the ascent above the Onomichi Channel.

From below, the structure appears as a spiral of concrete and steel hovering over the slope. The circular ramp rises from ground level in a slow curve, and simply walking up that spiral becomes part of the view. People circle the platform at different speeds and directions, and watching them trace the curve adds a human rhythm to the static line of the hills. At the top, the deck opens into a wide 180-degree panorama that takes in the channel, ship routes, and the tightly packed roofs of the town, designated as a Japan Heritage landscape.

The descent allows for a second, slightly different observatory experience. Stairs cut through the spiral, framing downtown Onomichi and the Seto Inland Sea at each landing. At some angles, the stacked curves of the structure become the foreground, with bridges, shipyards, and islands unfolding behind; at others, the architecture almost disappears into the slope, leaving only railings and sky. In the summer months, the sound of wind chimes from nearby Senkoji drifts up the hill, reminding visitors that the observatory is part of a wider park and temple environment, rather than a standalone object, a point along a route rather than a final destination.

Kirosan Observatory (Ehime) | Kengo Kuma’s “Invisible Architecture”

Kirosan Observatory sits at the end of a winding mountain road above the Kurushima Strait, yet the structure itself keeps a low profile. Designed by Kengo Kuma as an exercise in “invisible architecture,” it uses weathering steel that darkens over time, allowing the platforms and railings to recede visually into the hillside. From a distance, the geometry almost dissolves into the slope; up close, it feels like a series of paths and ledges carved out to meet the sky.

On clear days, the reward is immediate. The Kurushima-Kaikyo Bridge stretches across the water in a sequence of bold white spans, hopping from island to island toward Imabari. Ferries, cargo ships, and fishing boats mark slow routes through the Seto Inland Sea, and the surrounding hills roll away in overlapping shades of green and blue. The light changes quickly here; late afternoons can bring strong reflections on the water and dramatic color shifts as the sun drops toward the horizon.

Mist and rain tell a different story. When clouds descend over Kirosan, visibility may shrink to almost nothing, and the observatory becomes a quiet platform suspended inside a white field. In these conditions, Kuma’s ambition to erase the boundary between building and environment becomes very literal: steel, concrete, sky, and fog merge into a single, muted space.

The layout encourages unhurried circulation, as multiple levels connect by ramps and stairs, leading to a long wooden platform and rough stone blocks placed for sitting. A small secondary lookout further down the slope frames another angle on the bridge and islands. Signage remains minimal, so the focus stays on wind, temperature, and the wide arc of the strait below. Most visitors arrive by car or tour bus, yet the experience on the platform belongs entirely to those willing to stand still and let the view work on them.

Sasayama Castle Oshoin (Hyogo) | A Monument of Samurai Culture and Architectural Renewal

On the broad plains of Tambasasayama, Sasayama Castle Oshoin stands at the heart of a former castle complex that once controlled three baileys — Honmaru, Ninomaru, and San-no-maru — laid out as a strategic base between Kyoto and the powerful domains of Western Japan. The Tokugawa shogunate positioned it as a key outpost linked to the defence of Osaka Castle, and traces of that political network still show in the massive stone walls. Looking closely at the blocks, visitors can find over 150 carved symbols left by different feudal lords who contributed to the construction: a quiet yet eloquent display about the influence of each lord and the authority of the Daimyo in the rock itself.

The current building is a careful reconstruction completed in 2000, based on original blueprints and a detailed wooden model created by a miyadaiku master carpenter. The first Oshoin, completed in 1609, burned down in 1944.

Architecturally, Sasayama Castle Oshoin is a rare, large-scale example of formal samurai residential design, comparable in size and presence to the Tozamurai reception hall at Nijo Castle’s Ninomaru Palace. Its plan separates the official audience halls from the more private receiving rooms of the domain lord, who had his residence elsewhere on the grounds. The grand entrance borrows cues from aristocratic homes, while the most formal chamber follows shoin-zukuri conventions: a special pine tree painting behind the lord’s seat and an elaborately decorated ceiling signal that this is where the highest-ranking guests were received.

Today, seasonal maple and cherry trees frame the approach to the Oshoin, softening its martial past. Visitors wander through the halls, examine the reconstruction model, try on samurai costumes, or look out toward the town streets, reading the building as both a historic stage and part of a living castle town.

WEEK Kamiyama (Tokushima) | A Creative Retreat Breathing Life into the Mountains

Set beside the clear flow of the Ayukui River, WEEK Kamiyama brings together a renovated 60-year-old kominka and a low, glass-fronted lodging wing, forming a small riverside base for people who want to stay in Kamiyama at local speed. The former family home now works as reception, dining room, and commons: guests check in, sit down at shared wooden tables, and eat meals cooked from produce grown in the area. Smoke-darkened beams and hand-cut joints remain visible overhead, and a simple shop gathers regional products and independent publications that echo the place’s values of usefulness and care.

Across the yard, the accommodation wing faces the river in a single, quiet line. Built from local cedar and cypress, it contains eight rooms in five layouts, from compact doubles to a larger group room. All share the same basic palette of wood, white walls, and river light, with floor-to-ceiling glazing that frames the foothills and pale stones of the riverbed. A room with a desk running along the windows for those working remotely, while a small lounge offers a record player with some available vinyl, and clearly labeled recycling reinforces the sense of an everyday house scaled for guests.

Around WEEK Kamiyama, the rest of the town’s creative ecosystem flourishes, welcoming remote workers, creative professionals, and Shikoku 88-temple pilgrims who pause here to rest between stages of their own routes. The lodging is booked directly via its website, rather than through major platforms, thus keeping communication close between hosts and guests. Architecture, in this case, becomes a framework for shared time by the river, holding together the rhythms of work, conversation, and unhurried days in the mountains.

A Journey of Coexistence Between Nature, People, and Architecture

The buildings featured here are places to feel a connection with the landscapes that surround them. Each design reflects both a local sensibility and a modern aesthetic, achieving harmony rather than dominance. Architectural works are completed only through the relationship with their environment. These are best experienced not in isolation, but alongside the nearby natural scenery and cultural sites that give them meaning.
Travelling through these five locations creates a quiet thread across Setouchi: each place responds first to its setting and only then to its role as a “spot” on a map. Taken together, these sites present Setouchi as a region where architecture grows out of its surroundings, inviting visitors to pay attention not only to the structures themselves, but to the sea, mountains, and communities that sustain them.