裂 Seki Onsen Kumo Hō Sō

The outdoor bath sits across a footbridge from the main building, built from granite boulders beside the river and split into two pools, one hotter and one milder. Bathing there is mixed, with a women-only stretch in the evening and a bathing wrap available for anyone who wants one. The indoor bath, known as Kajika-buro (かじか風呂), is carved into the natural granite bedrock and swaps between the men's and women's sides through the day; some guests alternate that heated water with a separate, unheated mineral-spring pool nearby. The spring itself is strongly alkaline, leaves skin noticeably smooth, and runs on the cooler side, so you can soak a long while without getting light-headed. Sakeishi Onsen Unposo is an old wooden ryokan down a steep, narrow road by the river at the foot of Mt. Daibosatsu, part of the national network of small, out-of-the-way hot-spring inns. Rescued cats and dogs wander the grounds, and more than one guest has said it feels like coming back to their own family home.