Kinugawa Onsen Isshinkan

A century-old, 39-room family inn with its own spring, a nine-tub 'kurhaus' bath, a warm-spring swimming pool and dinners served in private rooms — the building is tired, the water runs lukewarm, and some river-view rooms look out at an abandoned hotel

Isshinkan opened in 1922 as a kappō restaurant; the inn tells how, some 20 years later, the owner Numao Hironosuke found one snow-free patch on the Kinugawa riverbank, warm to the touch, and the restaurant became an inn with its own hot spring. Today it's a 39-room, almost entirely tatami house on the gorge. The draw is the water and the variety: the spring (alkaline simple, 34°C at source, no water added) feeds a 'kurhaus' of standing, lying, jet and box-steam baths, a sauna, a covered rock bath, a bookable riverside private bath and a 10 m indoor spring-water pool. Most recent evidence comes from booking-site reviews rather than blogs. Japanese guests rate it 4.17 across 901 reviews on one major site (dinner 4.37, service 4.35, facilities 3.87) and 3.8 across 573 on another (rooms and cleanliness 3.5). They praise dinners and breakfasts served in private or semi-private rooms, a choice of set menus per person — the tomato-broth Tochigi wagyu hotpot is the signature — roomy two-room suites, good rice and kind, attentive staff; a 2023 blogger called the bath 'a little spa' and a March 2026 blogger called the dinner lavish. The complaints, from late 2025 to October 2026: an old building with mouldy ceilings in a corridor and one room, lukewarm baths, a rock bath shut for a leak in September 2026 without notice, thin shabu-shabu portions, cold grilled fish, karaoke noise and the derelict hotel across the river. Two-meal stays ran about ¥16,000–28,000 per person in 2026.