Kaikayu is a communal bathhouse located in Andai Onsen within the Yudanaka Shibu Onsen area of Yamanouchi Town, Nagano Prefecture. Andai Onsen dates back to 1705 when a bathhouse was established on the riverbank of the Yokoyu River, and has flourished as a therapeutic bathing destination since the Edo period. Kaikayu is the second communal bathhouse located near Andai Ooyu. It features black wooden walls and a concrete exterior, with a charming Showa-era orange door. The hot spring features sodium chloride-sulfate water with pH 8.3 from the Kyoekikai No.11 borehole, with a source temperature of 91.7 degrees Celsius, offered as free-flowing natural hot spring water. The mineral content is 1.623g per kg. The small tiled bathroom has the atmosphere of a local public bathhouse, perfect for experiencing an authentic Japanese bathing experience. The changing room and bathroom are separated by glass blocks with a small steam vent window. The water temperature can be adjusted via PVC pipes, normally around 40 degrees Celsius, rising to over 42 degrees when source water is added. It is more compact than Andai Ooyu and is exclusively for local residents and guests staying at Andai Onsen accommodations.