Kusatsu Onsen — Yumomi Ceremony and the Unique Acidic Famous Hot Spring

Nestled among the mountains of Gunma Prefecture at an altitude of 1,156 meters, Kusatsu Onsen is Japan's most storied hot spring destination, a town built entirely around the extraordinary thermal waters that have flowed here since ancient times. The name "Kusatsu" may derive from the Japanese word for "smells of grass" — a poetic reference to the sulfurous fragrance that drifts through the town from the legendary Yubatake, or "hot water field," where scalding spring water flows through a network of wooden channels in the heart of the town. This is a place where the relationship between people and their thermal springs has been refined over centuries into something approaching an art form.

Highlights

The yumomi ceremony is Kusatsu's most distinctive cultural tradition — a practice developed to cool the super-heated spring water (which emerges at temperatures of up to 95°C) without adding cold water, which would compromise the water's medicinal potency. Teams of women in traditional dress stir the water with long wooden paddles called "yumomi-ita" in a synchronized, rhythmic motion while singing traditional cooling songs (yumomi-uta) that set the pace of the work. The ceremony at the Netsu-no-Yu bathhouse runs several times daily and can be participated in as well as observed — visitors are invited to try the paddle for themselves, making for a genuinely interactive cultural experience.

Kusatsu's waters are among the most strongly acidic of any major hot spring in Japan, with a pH of approximately 2.0 — close to that of lemon juice. This exceptional acidity is credited with powerful antibacterial properties and benefits for skin conditions, and traditional records dating back to the Edo period document cases of recovery from various ailments attributed to the waters. Modern visitors come for the relaxation as much as the therapy, but the sense of bathing in something genuinely medicinal adds a dimension of mindful intention to the experience.

The town itself is a pleasurable destination beyond the baths, its streets offering handmade crafts, local sake, Kusatsu's signature Onsen manju steamed buns, and the kind of atmospheric old-town character that makes walking from shop to shop as enjoyable as the spa itself. The Yubatake, lit up at night, provides a dramatic and photogenic focal point for evening strolls.

Getting There & Tips

- Access via JR Agatsuma Line to Nagano-hara-Kusatsu-guchi Station, then a 25-minute bus to Kusatsu; or direct highway buses from Tokyo (approx. 3.5 hours) - The Netsu-no-Yu yumomi demonstration is held multiple times daily; check the schedule at the facility - Participation in the yumomi ceremony costs approximately ¥600; observation is included with the bathing fee - Seven free public baths (Soto-yu) are maintained by the town for visitors; towels must be brought or purchased nearby - Onsen manju from local shops near the Yubatake make ideal warm snacks and souvenirs

Best Time to Visit

Winter evenings are the most atmospheric time to visit Kusatsu, when the steam rising from the Yubatake mingles with falling snow and the illuminated channels glow amber against the dark sky. Summer brings relief from the heat of the lowlands and the annual International Music Festival. The town is busiest during Golden Week (early May) and the New Year holiday period, when advance booking is essential.