The clue to this area's mystique lies in its name, Kawayu Onsen, or hot water river. Thermal water bubbles up from the river bed, allowing for hot-water bathing in a natural setting. Squeezed in between lush green mountain slopes and a huddle of hostels and inns, river relaxation is the order of the day.
If you are looking for a relaxing dip outside of those months, shovels are available for you to dig your own bathing spot. There are also some pre-dug baths for those who want to get right in.