Akagi-san (赤城山, 1,828 m) is a large stratovolcano in Gunma Prefecture, listed by the Japan Meteorological Agency as an active volcano. Roughly 25 km across at its base, it is a composite volcano with summit calderas and central cones rather than a single peak — the name "Akagi-san" refers to the whole massif. At its heart sits Ōnuma (大沼), a caldera lake at about 1,345 m and one of the largest crater lakes in the Kanto region. A road and a year-round bus reach the lakeshore, from which the highest summit, Kurobi-dake, is a climb of about 500 m on foot. Akagi-san is counted, with Haruna and Myōgi, among the Jōmō Sanzan — the Three Mountains of Jōmō (old Gunma).
Why Fukada Chose Akagi-san
Kyuya Fukada included Akagi-san in Nihon Hyakumeizan. The book runs in a broadly north-to-south sequence — Akagi-san sits between Hotaka-yama and Kusatsu-Shirane — and is not a quality ranking.
Akagi-san earns its place through scale and character rather than altitude: a broad volcanic massif crowned by a caldera holding a permanent lake, ringed by a cluster of distinct peaks, and long woven into the folk culture of Gunma as one of the Jōmō Sanzan.
The Mountain
| Feature | Detail |
|---|---|
| Highest point | Kurobi-dake (黒檜山), 1,828 m (5,997 ft) |
| Volcano type | Composite stratovolcano with summit calderas; JMA active volcano |
| Prefecture | Gunma |
| Caldera lake | Ōnuma (大沼), ~1,345 m; smaller crater lake Konuma (小沼) nearby |
| Other rim peaks | Komagatake 1,685 m, Jizō-dake 1,674 m, Chōrōjisan 1,579 m |
| Book position | Included (book order is roughly north-to-south, not a ranking) |
| Typical season | May – November; winter access possible with studless tires |
The massif is not one summit but a ring of peaks around the calderas. Kurobi-dake (1,828 m) is the highest, with Komagatake (1,685 m), Jizō-dake (1,674 m) and Chōrōjisan (1,579 m) on the rim, and the two crater lakes — larger Ōnuma and smaller Konuma — below.
The Routes
Flagship Loop: Kurobi-dake + Komagatake
Grade: Moderate
- Distance: ~5.0 km loop
- Elevation gain: ~560 m cumulative
- Time: ~3.5 hours
- Character: From the Kurobi-dake trailhead at Ōnuma (~1,345 m) up to Kurobi-dake (1,828 m), across to Komagatake (1,685 m), then down to the visitor-center area. A steady, well-walked climb on a clearly defined trail with strong summit views.
Lakeside Walk: Ōnuma Shore
Grade: Easy
A flat walk around the shoreline of Ōnuma at about 1,345 m. No significant climbing, suitable for all fitness levels, and a good option for visitors not attempting the summits.
Getting There
From Maebashi (Gunma):
A Kan-etsu Kotsu direct bus runs year-round from Maebashi Station to the Ōnuma / visitor-center area (during the visitor-center rebuild from 2025 the terminus is "Akagi Hiroba-mae"). By car it is a mountain drive of roughly 45 minutes to the lakeshore.
From Tokyo:
JR Joetsu Shinkansen to Takasaki, or local trains to Maebashi, then the Akagi bus. The prefectural road tops out at Ōnuma; the summit itself is reached only on foot.
Flora and Wildlife
Asiatic black bears (ツキノワグマ): Asiatic black bears inhabit the forested zones below the caldera. Carry a bear bell on trails away from the busy lakeside. This is Honshu — there are no brown bears here, so bear spray is not part of standard practice for this mountain.
Azaleas — a season-long succession: Akagi-san is known for azaleas that bloom in waves through late spring and early summer, from Akayashio through to Rengetsutsuji. The signature display is the Rengetsutsuji (Japanese azalea) at the Shirakaba Pasture (白樺牧場), where roughly 100,000 plants peak in early-to-mid June. The pasture interior is only entered on special tours, but the grounds are clearly viewable from the fence and observation deck.
Ōnuma caldera lake: The lake's signature fish is wakasagi (Japanese pond smelt). Ōnuma is one of the few lakes in the Kanto region where you can fish for wakasagi through holes drilled in the ice, a winter tradition running from about early January to late March (a small permit, around 800 yen, is required).
Summit views: On clear days the panorama from the Kurobi-dake area takes in the Tanigawa range, Hotaka-yama, Sukai-san and the Nikkō mountains, with the distant Northern Alps and Yatsugatake beyond. Toward the Jizō-dake direction, Mt. Fuji is visible on the clearest days, and Tokyo Skytree can occasionally be picked out across the Kanto plain.
Seasonal Guide
May – June: Azaleas in succession, building to the Rengetsutsuji peak at Shirakaba Pasture in early-to-mid June. The most colourful season; weekends draw crowds.
July – August: Humid on the lower approaches, but the caldera area at altitude stays comparatively comfortable.
September – October: The clearest air of the year and autumn colour across the caldera forest.
Winter: Ōnuma freezes and the on-ice wakasagi fishing season runs from about early January to late March. The road stays generally open and the Maebashi bus runs a winter schedule, but the mountain is 10–15°C colder than central Maebashi and the access road carries snow and ice.
Practical Tips for Foreign Visitors
Year-round bus access: The Kan-etsu Kotsu bus from Maebashi reaches the lakeshore area through all seasons, making Akagi-san feasible without a car. Check the current terminus, which is "Akagi Hiroba-mae" during the visitor-center rebuild.
Winter driving: If you drive in winter, studless tires are mandatory on the mountain road and ice is routine. Dress for temperatures well below those in the city.
Azalea-season lodging: Book accommodation weeks ahead for late-May and early-June weekends, when the Rengetsutsuji display draws heavy visitor numbers.
Maebashi: The Gunma prefectural capital makes a useful base. The Maebashi Sericulture Memorial Museum in Shikishima Park displays tools and machinery from the area's silk-reeling history; the region's World Heritage silk landmark, the Tomioka Silk Mill, lies further afield.
Frequently Asked Questions
Can you climb Akagi-san without a car?
Yes. A Kan-etsu Kotsu direct bus runs year-round from Maebashi Station to the Ōnuma / visitor-center area, so the mountain is feasible without a car. During the visitor-center rebuild the terminus is "Akagi Hiroba-mae." From Tokyo, take the JR Joetsu Shinkansen to Takasaki (or local trains to Maebashi), then the Akagi bus.
Is Akagi-san a day hike or an overnight trip?
It is a day hike. The flagship Kurobi-dake + Komagatake loop from Ōnuma is about 5.0 km with roughly 560 m of cumulative gain and takes around 3.5 hours. Vehicles reach Ōnuma at about 1,345 m, leaving roughly 500 m of climbing on foot to the highest summit.
When is the best season, and what about the azaleas?
May through November is the typical hiking season, and September–October brings the clearest air of the year along with autumn colour. The most colourful time is May–June, when azaleas bloom in succession and the Rengetsutsuji display at Shirakaba Pasture peaks in early-to-mid June; weekends then draw crowds, so book lodging weeks ahead.
Are there bears on Akagi-san, and do I need bear spray?
Asiatic black bears live in the forested zones below the caldera. Carry a bear bell on trails away from the busy lakeside. This is Honshu with no brown bears, so bear spray is not part of standard practice for this mountain.
Is Akagi-san suitable for an easy outing?
Yes. A flat walk around the shoreline of Ōnuma at about 1,345 m involves no significant climbing and suits all fitness levels — a good option for visitors not attempting the summits. In winter, Ōnuma freezes and on-ice wakasagi fishing runs from about early January to late March (a small permit, around 800 yen, is required).
This guide is part of the Japan's 100 Famous Mountains: Complete Hyakumeizan Guide series.
