Zao Onsen Uta no Yado Wakamatsuya

A 21-room inn tied to the poet Saitō Mokichi, with its own unwatered, unheated pH 1.8 sulphur spring, two free private baths and Yamagata-beef kaiseki in private dining rooms — the building itself is newer and some fittings are tired

Wakamatsuya traces its founding to 1655 and calls itself the inn of Saitō Mokichi (1882–1953), the Yamagata-born tanka poet who was related to the owners' family and often stayed; Mokichi's own calligraphy hangs in a small gallery, and guests are handed paper strips to write their own poems, which line the corridors. The inn has since moved into a newer building, so the history is in the displays rather than the architecture. The draw is the water: the inn's own strongly acidic sulphur spring (pH 1.8), which the inn says reaches the baths with no added water, no heating and no recirculation. There's a shared indoor bath, two outdoor tubs including one carved from an 18-tonne Zao boulder, and two private family baths that are free, unbookable and open 24 hours. Japanese guests rate it 4.75 across 832 reviews on one major site (service 4.78, dinner 4.68) and 4.8 across 1,144 on another; most of the recent evidence comes from these booking-site reviews, backed by two first-hand blogs from 2022 and 2025. They praise the warm staff, kaiseki served in private rooms, and a lounge with free drinks, bottled milk and handmade sweets all day. The complaints, mostly from 2024–2026: dinners some find unremarkable or slow-paced, a sparse breakfast, a cramped changing room and weak showers, central air conditioning that can't be adjusted, a burst pipe that left one March 2025 guest without water, and a leaking air-conditioner in a suite in September 2026. Standard two-meal plans run about ¥26,000–35,000 per person.