Saiko Bat Cave(西湖蝙蝠穴, saikokoumoriana) is the biggest cave around Mt. Fuji, and it has over 350 m length. This cave is made by Mt. Fuji’s lava. So, entire grand and walls formed instant cool down of lava. Because the temperature in the cave is very steady through the year, it becomes nests for natural bats. There are three kinds of bats inhibit in this cave.
There many lava domes, lava stalactite and lava plates in this cave.
Tourist Info.
There is parking and restroom
Admission fee: 300 yen for adult, 150 yen for kids. There is a group discount from 20.
Open: 9:00 to 15:00, 3/20 to 11/30
Access
0. at Kawaguchiko Station
1. use local bus to Fuketsu mae.
2. walk north (20 min.)
300 JPY
30 min
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映画好き集まれ！ 
Saiko Bat Cave is the one of the National Monument of Japan and located in Aokigahara Jukai, right next to Lake Sai. Deep side of the caves are preserved for wild bats, but there are stairs, floors and lights are set for visitors. So, you can enjoy small venture in this cave. You have to be careful when you entire this cave because floor is slippy and top is very low.
The admission office will rent you the helmet for your safety.
Phone: 0555.82.3111
FAX: 0555.82.3112