Kotan Onsen Hot Spring

A free open-air rotenburo (露天風呂) right on the shore of Lake Kussharo, carved from the lakebed rock. The water is a sodium bicarbonate spring, soft and warming. The divider between the mixed and separated sides is literally a single rock, so it is quite relaxed; changing rooms and toilets are nearby. In winter the hot spring seeps into the lake edge and draws swans, making for an unforgettable backdrop.