Nasu-Onsen Shinshun no Kago Hewitt Resort

Every room at this ryokan-style resort in the Nasu Highlands comes with its own private onsen, partly open to the forest air, plus cedar paneling and bespoke bedding for when you finally step out. Minimalist design and floor-to-ceiling glass keep the surrounding woodland front and center. The communal library stocks art books and Karuizawa whiskies beside a fireplace, which is either meditative or dangerously comfortable, depending on your schedule.