Doroyu Onsen Okuyama Ryokan

Doroyu, the name means "mud hot spring", sits in a Tohoku mountain valley with naturally hot ground and fumarolic activity all around. The ryokan draws three different springs into separate baths: two kinds of sulfur water and a simple spring, which means you can actually compare different sulfur compositions in one visit. The mixed-gender outdoor rotenburo is cloudy white and smells of sulfur, with two pool levels set into the hillside.