Saiko Bat Cave was added to Your Favorites!
Fuji-Hakone-Izu NP, Yamanashi
Claim this place to tell your story your way.
A 2008 survey confirmed 4 bat species roosting here. On April 16, researchers counted about 340 lesser horseshoe bats emerging from a passage too small for people to enter—the cave’s busiest roost is hidden from visitors.
A government monument report recalled thousands of bats hibernating here in the 1920s. It also records bats being captured in winter, charred as a folk remedy then believed to treat women’s illnesses, and shipped to the Keihin region.
Saiko Bat Cave formed in lava from Fuji’s 864–866 Jōgan eruption. That same eruption split the ancient lake Senoumi, leaving today’s Saiko, Shōjiko and Motosuko; the cave is a hollow trace of the lava flow.
The cave stays warm enough in winter not to freeze, making it a hibernation refuge. After human disturbance once brought bats close to extinction, a protected zone was established deep inside; the bats are recovering, and winter access is closed for their protection.
At about 350 meters long, Saiko Bat Cave is the largest lava cave at Mt. Fuji’s foot. Its 2- and 3-tier lava shelves preserve traces of different lava-flow levels, while lava “stalactites” hang from the walls and ceiling.
On December 17, 1929, Japan designated this natural monument under a name that explicitly includes both the cave and its bats: “Saiko Bat Cave and Bats.” It opened to visitors in April 1998.
