Sengairei

Sengairei (2,734 m) straddles the boundary of Iijima Town and Ōkuwa Village in Nagano Prefecture and is one of Japan’s 100 highest mountains (ranked 82nd by elevation).
It rises on the southern main ridge of the Kiso Mountains (Central Alps), a sharp, spire-like rock peak between Mount Kosumo and Mount Minamikoma, with a knife-edge granite ridge and chained sections that make it one of the toughest passages in the Central Alps. There is no trail that climbs Sengairei on its own; it is reached as a waypoint while climbing Mount Kosumo or Mount Minamikoma, or while traversing the ridge.
There is no public bus to the trailhead, so a taxi from Suhara Station on the JR Chūō Main Line is the standard option. From Suhara Station, take a taxi to the Inagawa Dam area.

The trailhead is the Kosumo trailhead (above Inagawa Dam, about 1,160 m). The standard route is Kosumo trailhead → Fukutochi Bridge → Kosumo Hut (overnight) → Mount Kosumo → Sengairei. Day one takes about 5–6 hours to the hut; a day trip is not possible, so this is an advanced route requiring one night on the mountain. Most hikers continue over Sengairei to Mount Minamikoma and back.
The Inagawa forest road has been closed to vehicles below Inagawa Dam since the 2018 storm damage (no reopening date as of 2026); taxis and private cars can only reach the area below the dam, adding about one hour of walking to the trailhead. The Kosumo Hut is closed for the 2026 season (no reopening date set), but the adjacent Kosumo emergency shelter (unstaffed) is available. The rocky, chained ridge linking Mount Kosumo, Sengairei and Mount Minamikoma is among the most rugged in the Central Alps; the climbing season runs from July to early October. Always check the latest forest-road, trail and hut conditions before you go.

*Information last verified: June 14, 2026

How to access the trailheads

1. [Round trip] Suhara Station → Inagawa Dam → Kosumo trailhead

1. [Round trip] Suhara Station → Inagawa Dam → Kosumo trailhead

Suhara Station on the JR Chūō Main Line (Chūō West Line) is the gateway. There is no bus to the Kosumo or Minamikoma trailhead, so a taxi or private car is the only option.

① Suhara Station → below Inagawa Dam (taxi)
Take a Nagiso Kankō Taxi from Suhara Station toward the Inagawa Dam area. The fare is roughly ¥6,000. No taxis wait at Suhara Station, so booking in advance for both legs is essential. You can also board at JR Ōkuwa or Nojiri stations.
― Nagiso Kankō Taxi 0264-55-4155

② Below Inagawa Dam → Kosumo trailhead (about 1 hour on foot)
The Inagawa forest road is closed to vehicles below Inagawa Dam due to the 2018 storm damage, so the upper parking area is unusable. Taxis and private cars can only reach a point about 1 km below the dam, from where it is about a 1-hour walk along the forest road to the Kosumo trailhead (about 1,160 m). Work back from your descent time and book the return taxi with plenty of margin.
Note that the route via Usagidaira toward Mount Higashikawa and Mount Utsugi beyond Inagawa Dam is closed (no foot access), but the routes to Mount Minamikoma, Mount Kosumo and Sengairei are open (as of April 2026).

Inquiries: For the latest forest-road and trail conditions, contact the Ōkuwa Village Industry & Tourism Division (0264-55-3080).

Reference: [Ōkuwa Village — Central Alps Climbing Information] / [Kosumo Hut information]

Climbing routes and safety notes

Route: Kosumo trailhead → Fukutochi Bridge → Kosumo Hut (2,340 m, overnight) → Mount Kosumo (2,613 m) → Sengairei (2,734 m) → Mount Minamikoma (2,841 m). Day one takes about 5–6 hours to the hut; on day two you follow the ridge. As a guide, about 1 hour from Kosumo Hut to Mount Kosumo, about 1 hour 30 minutes from Mount Kosumo to Sengairei, and about 50 minutes from Sengairei to Mount Minamikoma. There is no trail to Sengairei alone; you reach it on an out-and-back from Mount Kosumo or while traversing to Mount Minamikoma.

Rocky ridge and chains: Sengairei is a sharp, spire-like rock peak, and the section between it and Mount Minamikoma in particular is a steep knife-edge ridge with a series of chains. The western face drops away in cliffs toward the Kesasawa valley, and the risk of a fall or losing the route rises sharply in rain, strong wind or fog. Do not push on—turning back is a valid decision. Keep three points of contact, and carrying a helmet is reassuring.

Huts and emergency shelter: The Kosumo Hut is closed for the 2026 season (no reopening date). The adjacent Kosumo emergency shelter (unstaffed) is available, but bring your own water, food and bedding. Check the latest operating status before you go.
― Kosumo Hut (reservations/operation) 090-7699-9337

Gear and season: The season runs from July to early October. Carry water, food, rain gear, warm clothing, a headlamp and a map/GPS. Bear sightings are increasing, so take precautions such as a bear bell.
Emergencies: In an accident, call 110 (police) or 119 (fire/rescue).
・Kiso Police Station 0264-22-0110

Photo by Alpsdake / Wikimedia Commons, CC BY-SA 3.0