Tsukioka Onsen Mashu

Mashu is a 38-room ryokan in Tsukioka Onsen where the open-air baths run undiluted, emerald-green sulfur water straight from the source. The indoor baths, by contrast, use heated tap water rather than the spring. There are four outdoor baths split across two bathing halls that swap between men and women depending on the time of day, plus a small reservation-only private bath lined with Sado akadama stone. Renovated in 2018, the inn leans quiet and couples-oriented rather than group-focused, with a garden-facing lounge for unwinding after a soak. It takes overnight guests only; day-use bathing isn't offered.