Nakabusa Onsen

A Mountain Spa at the Foot of Mount Tsubakuro

Nakabusa Onsen (中房温泉) is a hot spring settlement in Hodaka Ariake, Azumino City, Nagano Prefecture, which opened as a healing spa in 1821 at the trailhead for Mount Tsubakuro in the Northern Alps, and seven of its structures were registered together as Registered Tangible Cultural Properties on 25 July 2011. The owner, Nakabusa Onsen Co., Ltd., still runs it as an inn.

Local legend reaches much further back. In 804, the story goes, the general Sakanoue no Tamuramaro stopped here on his campaign to the northeast, killed a demon chieftain known as Giseiki Hachimen Daio who had been tormenting the villagers, and healed his wounded soldiers in the hot water. The inn still tells this as the origin of the springs.

The documented history starts with alum. In 1821 Momose Mohachiro, acting on orders from the Matsumoto domain, came up the valley to mine the mineral and built a bathing hut at the same time. Alum gave raw silk its sheen, and silk was the domain's most valuable product. According to geologist Otsuka Tsutomu of Shinshu University, the springs here alter the surrounding granite, and hot water seeping out through the cracks evaporates in the ground heat and leaves alum crystals behind. The mine and the spa, in other words, came from the same rock.

Modern mountaineering changed Nakabusa's purpose. In 1909 Momose Isamatsu, the sixth proprietor, published a statement in the journal of the Japanese Alpine Club promising to open trails, set up signposts, standardise the pay of guides and porters, and build huts. Under his successor Momose Hikoichiro, a traverse was laid out along the ridges via Mt. Otenshō and Mt. Jōnen to Kamikōchi, and a chain of huts was planned toward Mt. Yari.

Walter Weston, the British missionary who introduced the Japanese Alps to the English-speaking world, stayed here in 1912. In 1918 the educator Sawayanagi Masataro, head of the Seijo school, brought pupils to Nakabusa for one of Japan's earliest open-air forest schools. By then the spa was a place to recuperate as well as a base for climbers.

Seven Buildings, Two Eras

The seven registered properties are the Main Building Kiku, the Former Yukaisho, the Tamura Yakushido, the Mountain God Shrine, the Large Hot Spring Pool, the Storehouse and the Itakura Storehouse. Their registration numbers run consecutively, 20-0372 to 20-0378, and all were recognised for their contribution to the historic landscape. Six are counted as single buildings; the pool is counted as one site.

Sorted by date, they fall into two clear groups. The older group belongs to the late Edo period: the Tamura Yakushido of 1848, the Storehouse of 1854, and the Itakura Storehouse and Mountain God Shrine, both dated only to the end of the era. The newer group is modern: the Former Yukaisho and the Main Building Kiku from the Meiji era, and the stone pool of 1923.

Hoyano Shigeo, an architectural historian at Shinshu University, reads the two groups as evidence of two different mountain cultures. The Edo buildings belong to a world where livelihoods such as alum mining were bound up with faith. The Meiji and Taisho buildings belong to the age when climbing and resort life tied the mountains to the cities. On one small site you can follow, building by building, the spa's change from a mining outpost to a base for climbers and a summer retreat.

How the Site Is Laid Out

All seven properties sit within about 100 metres of each other, east to west. The Main Building Kiku stands toward the east, with the Former Yukaisho to its southwest, the Itakura Storehouse to its east and the Storehouse to its southeast: a Meiji guest building ringed by two late Edo stores and a Meiji outbuilding.

About 50 metres west of that cluster is the Tamura Yakushido, and just beyond it, on top of a great carved boulder, the Mountain God Shrine. This pairing of a small hall tied to the spring's origin legend and a shrine to the mountain deity occupies the middle of the grounds. Further down to the southwest lies the stone-walled Large Hot Spring Pool.

Behind the buildings are the spring vents themselves, and deposits of colloidal silica and siliceous sinter left by the water as it cools, a feature separately protected by the national government. Steam and the smell of sulphur follow you as you walk. The buildings were placed where the hot water rises, and they still gather around it.

Visiting, Bathing and Getting There

Nakabusa Onsen is a working inn, not a public park, so the registered buildings are seen by staying overnight or by booking one of the inn's day plans. The three-hour plan with a light meal costs 3,300 yen and the plan with dinner, allowing up to six hours on site, costs 6,600 yen; both include bathing, a geothermal steam-cooking session and a walk through the grounds with the sinter deposits and the registered buildings. Check-in for the three-hour plan runs between 10:00 a.m. and 3:00 p.m. Both require a reservation (tel. 0263-77-1488).

Beside the Mt. Tsubakuro trailhead is Yubara no Yu, a separate open-air bath for day visitors. Entry is 950 yen, with bathing between 9:30 a.m. and 5:00 p.m. (last admission 4:00 p.m.). It is for bathing only and does not include access to the grounds where the registered buildings stand.

The season runs from spring into late autumn. Prefectural Route 327, the only road up, is closed by snow roughly between the end of November and mid-April; in 2026 regular operation began in late April once the road reopened.

By public transport, start at JR Hotaka Station on the Oito Line. Minami-An Taxi runs a scheduled bus from the station to Nakabusa Onsen, about 55 minutes to the terminus, between late April and early November, with the timetable varying by day. By car, allow about an hour from the Azumino interchange on the Nagano Expressway. The road is narrow and difficult for large vehicles to pass on, and trailhead parking fills quickly on summer and autumn weekends.

Heavy rain sometimes brings the road down: in the summers of 2025 and 2026 it was closed or restricted for extended periods. Check the inn's website and the road information of the Nagano Prefecture Azumino Construction Office before setting out.

No published rule covers photographing the buildings. Around the baths and the pool, take care to keep other bathers out of your frame.