Lake Sai (西湖, Saiko) is the middle of the Fuji Five Lakes. It is unique from the other lakes in that it is surrounded by steep, wooded slopes on all sides, and Mount Fuji is only clearly visible from its western point. Like its neighbours, Shojiko and Motosuko, Lake Sai was formed as a separate lake from an eruption of Mount Fuji in the 9th century.
There are some camping sites around the shoreline and a hand full of coffee huts and restaurants, as well as a small village at the western end, but Saiko is noticeable less developed than Lake Kawaguchi. Slightly to the south visitors can find the Narusawa Ice Cave, Fugaku Wind Cave, Lake Saiko Bat Cave, and the infamous Aokigahara Jukai forest.