Kakuma Onsen Iwayakan

The mixed outdoor bath at this lone inn in Kakuma Gorge (Nagano) is fed by an iron-rich sodium bicarbonate-chloride spring that turns a warm amber-brown on contact with air, the cloudiness makes mixed bathing feel easy and natural. The source runs tepid at around 34-37 degrees in the tub, ideal for a long soak. The inn sits in what locals call the hidden hot spring of the Sanada clan's home territory, and the gorge setting lives up to that reputation.