From Kawaguchiko Station on the Fuji-Subashiri Electric Railway Kawaguchiko Line, take the Retro Bus Saiko-Aokigahara Line to the Saiko Koumori-ana bus stop.
Alternatively, take the Saiko Minshuku-mura bound bus to the Koumori-ana entrance bus stop.
From the Kawaguchiko Interchange on the Chuo Expressway, it's approximately 13.1 kilometers (about a 25-minute drive). Show route
Op.Hours
9:00 AM - 5:00 PM (Last entry at 4:40 PM)
Cld.Days
Closed from December 1st to March 19th each year for bat protection.
Fee
Adults: ¥300, Children: ¥150
INFO
The cave is dimly lit and has some low ceilings, so helmets are provided for head protection. The terrain is uneven in places, so comfortable walking shoes are recommended.
Saiko Koumori-ana (Saiko Bat Cave), located in Fujiyoshida-cho, Yamanashi Prefecture, is a lava cave renowned as a bat habitat. Designated a National Natural Monument, the cave, formed by a Fuji volcano lava flow, showcases unique formations such as lava domes and rope-like lava – characteristic features of lava caves. It offers a thrilling cave exploration experience while also allowing you to enjoy the abundant nature of the Aokigahara Forest.
Saiko Koumori-ana was formed by lava flows from the Jogan eruption, which occurred between 864 and 866 AD. With a total length of 386.5 meters, it's one of the largest lava caves in the Fuji Five Lakes area, boasting a complex, three-dimensional structure with multiple branching tunnels.
The cave features numerous formations typical of lava caves, including lava domes, rope-like lava, and lava shelves. Lava domes were formed when gases, primarily water vapor, accumulated in one place during the cave's formation. A lava dome approximately 1.5 meters in diameter and 50 centimeters high is found near the center of the cave's largest hall. Rope-like lava, showcasing the direction of the lava flow, is one of Saiko Koumori-ana's most iconic features. This formation occurs when less viscous lava flows on a gentle slope; the surface cools and solidifies while the interior remains molten. The solidified upper layer stretches, creating a ribbed texture similar to multiple ropes twisted together.
The cave's stable year-round temperature once supported a large bat population using it for hibernation. However, development around the cave and unregulated access led to a significant decline in the bat population. Since the 1990s, conservation efforts have gradually led to a recovery in the bat population. Two sections of the cave are now protected areas with wooden fences restricting access to safeguard the bats.
Saiko Koumori-ana offers more than just cave exploration; it's an opportunity to immerse yourself in the rich natural beauty of the Aokigahara Forest. Well-maintained walking paths wind through the forest, where you can observe the unique vegetation up close, with conifers such as Tsuga, Urajiro-momi, and Goyoma-matsu predominating alongside broadleaf trees including Mizunara, Konara, and Kaede, creating the characteristic dense, dark forest of Aokigahara.
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