Lake Saiko Bat Cave — Attraction in Fujikawaguchiko

Located in Aokigahara Forest near Lake Saiko, the Saiko Bat Cave is the largest lava cave formed by the eruption of Mount Fuji in 864 AD. The cave extends approximately 386 meters in total length and features several chambers and corridors with varying ceiling heights. It is part of the “Fugaku Wind Cave – Narusawa Ice Cave – Saiko Bat Cave” trio of lava tubes, all created by the same ancient lava flow.

The cave’s name comes from the bats that used to inhabit it, primarily the Eastern Bent-Wing Bats. However, the population has significantly decreased due to temperature fluctuations and human activity, and the cave is now mostly a geological site rather than a wildlife habitat.

Inside, visitors can observe fascinating natural formations such as lava ledges, lava shelves, and diatomite layers, which indicate the prehistoric water levels of the ancient Sea of Se-no-Umi. The cave’s temperature remains around 10°C (50°F) throughout the year, making it cool even during summer.

Illuminated pathways and safety railings make the route accessible, though some passages are narrow or require bending down. The cave tour takes about 15–20 minutes, and informative signs in Japanese and English explain...

This is the largest cave in the area, with multiple levels. There is a decent amount to see and learn about, and the free nature center attached to it makes it worth the visit. Inside the cave there is some signage in English, and some in only Japanese (no internet to translate either). There is a path that is easy and accessible, and an optional path with tunnels so small you almost have to crawl through them, which added to the fun factor for us.

More importantly, this area connects to a large network of trails through Aokigahara, an enormous old-growth forest that is breathtakingly beautiful. We used this cave as the starting point, then walked through the forest to the nearby Wind Cave (about an hour walk taking our time). There are maps all around and the trails are very well maintained and easy to follow. Taken as a whole, this was a really amazing day and well...

Very underrated place! The cave is in the middle of a volcanic forest, and is beautiful and serene. It's a nice, 8 minute stroll to the cave from the entrance. They lend you a helmet because parts of the cave are very low (and I'm not a tall person). The cave is fantastic, short, sweet, and cold. It's beautiful. One section, through the low path where you practically have to crawl, the cooled down lava rivets can be seen and are amazing. You can reach two little wooden doors, behind which are bats. You don't actually see any bats, because they are nocturnal. The point is to visit the cool cave, and allow for the bats to do...