Fuji Wind Cave: An Ice Cavern Left Wild Beneath Aokigahara
In December 1929, the old Ministry of Education placed three lava caves on Mount Fuji's northern slopes under protection on the same day. Two of them, Fugaku Wind Cave and Narusawa Ice Cave, went on to become well-lit visitor attractions with paved paths and ticket booths. The third, Fuji Wind Cave (Fuji Fūketsu), took a different path. Nearly a century later it remains undeveloped, reached only on foot through the forest, its floor sheathed in ice that the summer heat never fully reaches.
It is the largest of the cave's three siblings in terms of ice. Among the many lava caves scattered across the northern foot of Mount Fuji, none holds as much ice as this one, and in the hottest weeks of the year that ice barely retreats. The cave runs more than 230 metres, with a chamber 5 to 10 metres wide and a ceiling that averages around 5 metres, open enough that a visitor can walk through most of it standing upright.
A Cave Born From the Jogan Eruption
The story of Fuji Wind Cave begins with fire. In the year 864, Mount Fuji entered one of the most consequential eruptive episodes in its recorded history, the event Japanese sources call the Jogan eruption. Lava poured from vents on the volcano's northwestern flank and spread across the land below, burying a wide lake known as Senoumi and leaving behind the two smaller lakes that survive today as Lake Sai and Lake Shoji.
On top of that cooled lava, a forest slowly took root. This is Aokigahara, the so-called Sea of Trees, a woodland that grows directly over hardened basalt rather than ordinary soil. Tree roots crawl sideways across the rock instead of sinking into it, and the lava field is riddled with hollows and tubes.
Fuji Wind Cave is one of those tubes. As the 864 lava advanced, its surface chilled and crusted over while the molten rock beneath kept flowing. When the supply ran out, the still-liquid interior drained away and left a long corridor behind: a lava tube. The cave lies along the southern edge of the Aokigahara lava flow, near the foot of Omuroyama, a parasitic cone that the eruption's lava parted and flowed around.
Why It Became a Natural Monument
The 1929 designation document, written in the formal language of its era, set out a careful distinction between two kinds of volcanic cavity. The first is the lava tunnel: the drained corridor described above, often long and tunnel-shaped. The second forms when pockets of steam and gas collect inside a lava flow and the rock hardens around them, leaving smaller, irregular voids. The document noted that caves of this density and variety, clustered around a single volcano, are rare anywhere in the world.
Fuji Wind Cave was protected under the criterion for caves. Its value is partly geological, in that it is a clean, large-scale example of a lava tube preserved in close to its original condition, and partly a matter of what survives inside it. Because the cave has never been fitted with lighting, walkways, or handrails, the ice formations and lava textures stand much as they would have a century ago. For researchers studying how Mount Fuji's eruptions shaped the surrounding land, an undisturbed cave is itself a kind of record.
Inside the Cave: Ice, Basalt, and Silence
Entry is through a large collapse pit in the forest floor. From there the passage descends. The temperature drops quickly as you go down; readings near the entrance can sit close to zero degrees Celsius even when the outside air is well into the teens or higher.
The reward for the descent is the ice. The cave floor is covered by a thick sheet built up over many years, and from the ceiling hang columns of ice that catch what little light enters. Early surveyors compared the effect to a palace of crystal. Unlike the developed caves nearby, there are no spotlights here to stage the scene; the ice is simply what it is, lit by headlamps and reflecting back at odd angles.
The walls are basalt, dark and sound-absorbing. Visitors to lava caves often remark on how quiet they feel, and that is the basalt at work: the rock soaks up noise rather than echoing it. Along the passage you can read the flow itself in the stone: shelves where the lava level once paused, ropy ridges where the surface wrinkled as it moved.
This is not a cave dressed up for visitors. The ground is uneven, the ice is genuinely slippery, and parts of the route are low. That roughness is the point. Fuji Wind Cave offers something its polished neighbours cannot: a lava tube experienced on close to its own terms.
Around the Cave
Fuji Wind Cave sits within the Aokigahara forest, country that rewards slow walking. The approach follows part of the Shojiguchi trail, an old route up Mount Fuji, through woodland where the moss-covered lava and the sideways-reaching roots make the volcanic origin of the ground hard to ignore. The beech forest around Omuroyama is a recognised highlight of the area and a destination in its own right.
Travellers who want a cave experience without a permit and a hike have good options close by. Fugaku Wind Cave, roughly four kilometres to the northeast, is a 201-metre lava tube developed for general visitors, walkable in about fifteen minutes. Narusawa Ice Cave, a ring-shaped vertical cave, lies a short distance further on. Saiko Bat Cave, near Lake Sai, is another developed cave in the same forest. Together with Fuji Wind Cave, these sites show how differently a single eruption's caves can be presented, from a fully lit tourist route to an untouched hollow in the trees.
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Q&A
- Can I visit Fuji Wind Cave on my own?
- Not freely. The cave is undeveloped and protected as a Natural Monument, and entry requires advance permission. According to Yamanashi prefectural tourism information, visitors must file notification with the Fujikawaguchiko Town Board of Education before entering. Many people visit instead on a guided tour run by licensed local nature guides, who arrange the necessary permission.
- How is it different from Fugaku Wind Cave?
- They are separate caves with similar names. Fugaku Wind Cave is fully developed for tourism: paved, lit, with a ticket office and shop. Fuji Wind Cave has none of that. It is reached on foot through the forest, has no artificial lighting, and holds more ice than any other cave in the area.
- When is the ice at its best?
- Ice forms through the cold months and is most developed from roughly mid-winter into spring. Because Fuji Wind Cave retains so much ice, formations can persist into summer, though the exact extent varies year to year with weather and conditions inside the cave.
- How do I get there?
- The cave is in the Aokigahara forest at the northern foot of Omuroyama, reached via the Shojiguchi trail. The wider area is served from the Kawaguchiko area; the famous developed caves are about 15 minutes by car from the Kawaguchiko Interchange. There is no public transport to the cave entrance itself, and the final stretch is a forest walk.
- What should I bring?
- Treat it as a short hike into a cold, dark, uneven space. Sturdy non-slip footwear, warm layers, and a reliable headlamp are essential, since temperatures inside stay near freezing even in midsummer, and the ice underfoot is genuinely slick. A guided visit is the safest way to see it.
Basic Information
| Name | Fuji Wind Cave (Fuji Fūketsu) |
|---|---|
| Location | Kofu City, Yamanashi Prefecture (within the Aokigahara forest, northern foot of Omuroyama) |
| Designation | National Natural Monument, designated December 17, 1929 (criterion: caves) |
| Managing body | Kofu City (designated June 4, 1996) |
| Type | Basaltic lava tube, formed by the Jogan eruption of 864 CE |
| Scale | Total length over 230 m; width 5–10 m; ceiling averaging about 5 m |
| Access | Undeveloped; entry by advance permission only, via the Shojiguchi trail through the Aokigahara forest |
References
- National Database of Designated Cultural Properties — Fuji Fūketsu
- https://kunishitei.bunka.go.jp/bsys/maindetails/401/1104
- Cultural Heritage Online — Fuji Fūketsu
- https://bunka.nii.ac.jp/heritages/detail/138477
- Fuji-no-kuni Yamanashi Tourism Net — Fuji Fūketsu
- https://www.yamanashi-kankou.jp/kankou/spot/p1_4905.html
- Yamanashi Hiking Course 100 — Fuji Wind Cave and the Beech Forest of Omuroyama
- https://yamanashi-hiking100.jp/course/detail/51
- Yamareco — Fuji Fūketsu site information
- https://www.yamareco.com/modules/yamainfo/ptinfo.php?ptid=20115
Last verified: 2026.05.22