Lake Saiko Bat Cave

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 geological features.

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 worth doing.

A very nice cave inside a beautiful forest (actually part of Aokigahara Forest) that offers a standard route and a more difficult one. We, of course, decided to follow the more challenging one. It was worth it! We could walk over a petrified lava flow and other caves that supposedly host bats (we didn’t see any).

The bat cave is really cool and it's kind of nice to be able to go in a cave on your own and walk around. Please be mindful of the bats and quiet while you're walking around. You do have to get pretty low in some spots so definitely make sure you're wearing your helmet and be prepared to maybe get on your hands and knees. It is a little cold in the cave but it's nice in the summer. There's a bus stop out front and you can easily walk to the other caves from here

Nice site with a short walking trail leading to the cave. The cave itself has very low ceilings in several passages, and one section even requires crawling on your knees to get through. This part is not for everyone, but it can be skipped—though doing so makes the overall visit quite short. The main reception building , offers a unique exhibit featuring local fish as well as vintage Batman series posters. The staff are friendly and welcoming. Overall, worth a visit if you are nearby.

Worth a visit. The cave is beautiful, as is the surrounding forest. The cave path is really fun to do, but it has a very low ceiling in some areas, so requires appropriate clothing & footwear to enjoy. They provide safety helmets, but I was glad to have shoes with a grip on.

It’s very cool learning about how these caves were formed over thousands of years from the volcano. It’s probably not the best place to go if you’re claustrophobic. You’ll be squatting and walking for some distance. It’s cooler in the cave which was an amazing break from the blaring sun. Tickets are 350 yen and we were in and out in about an hour since we checked out the free museum (all in Japanese) and gift shop. The museum was interesting to learn about the fish conservation acts in Lake Seiko. Very helpful gentleman helping us during our time here despite the language barrier.

Caves formed from volcanic eruption now housing bats (albeit hidden away as to not disturb them). Pay the fee, get a helmet and go explore. Short walk through forest and then down into caves. One route is nearly on knees vs a normal walking route. Interesting to see but quite quick