Saiko Bat Cave

The Saiko Bat Cave, located near Lake Saiko in the Fuji Five Lakes region of Yamanashi Prefecture, is a natural lava cave formed by eruptions of Mount Fuji. The cave's origins trace back to the 864 AD eruption of Mount Fuji, when lava flows created an extensive network of underground passages in the area. This geological formation stretches approximately 350 meters in length, making it one of the more accessible lava caves in the region for visitors to explore.

The cave derives its name from the large bat population that historically inhabited the space, though fewer bats are seen today due to increased human activity and tourism. The interior maintains a consistent cool temperature year-round, typically hovering around 3 degrees Celsius, providing a stark contrast to outside conditions regardless of season. The cave's structure showcases distinctive lava formations, including rope-like patterns on the walls and ceiling that demonstrate the direction and flow of ancient molten rock.

Visitors can explore the cave through a self-guided walking route that takes approximately 15 to 20 minutes to complete. The pathway is relatively straightforward but requires some bending and careful footing due to low ceiling sections and uneven terrain. The cave interior is equipped with basic lighting, though bringing a flashlight is recommended for better visibility of the geological features. Hard hats are provided at the entrance and must be worn throughout the visit for safety.

The cave is accessible by car from central Fuji Five Lakes areas, located roughly 10 minutes by car from Lake Kawaguchi. Limited parking is available at the site. Public transportation options are limited, though some tourists combine visits with guided tours of the Aokigahara Forest, which lies nearby. Admission costs ¥300 for adults, making it an affordable addition to a Fuji Five Lakes itinerary.