Lake Saiko Bat Cave and Forest — Fuji's Hidden Lake

Lake Saiko, the fourth-largest of the Fuji Five Lakes, remains the quietest and least developed — no lakeshore hotels, minimal tourist infrastructure, and dense forest surrounding three-quarters of the shoreline. The lake sits at 900m elevation on the western side of Mt. Fuji, offering different viewing angles than the more famous Kawaguchiko. The area is known for the Saiko Bat Cave (西湖コウモリ穴), a 350-meter lava tube cave that houses colonies of Japanese long-eared bats, and the Aokigahara Forest which spreads from the southern shore.

The lake's western shore features the Saiko Iyashi no Sato Nenba, a reconstructed traditional village with 20 thatched-roof kayabuki houses that survived a typhoon in 1966. The houses now operate as craft workshops (pottery, weaving, glassblowing) and small museums displaying rural Yamanashi life. In winter, the village with snow-covered thatched roofs and Mt. Fuji beyond creates a scene from historical Japan.