The main sight of Yamanashi Prefecture is obviously Mt Fuji, Japans holy mountain. This huge volcano erupted in 864 with lava flows running down the north slope of the mountain. The lava flowed into Lake Motosu and Senoumi Lake, which was divided into three separate lakes by the lava. All three lakes are still connected by holes in the Lava stream and have the same water level all the time. The lava streams contain numerous lava tubes, some may be visited south of Saiko lake. All caves are rather cool, as they form cold traps, one is even called Ice Cave. During the Edo Period some of the caves were used to store food.