Kusatsu Onsen — Japan's Premier Hot Spring with the Highest Discharge Rate

High in the volcanic mountains of western Gunma Prefecture, Kusatsu Onsen has been celebrated as Japan's finest hot spring town for centuries, its waters ranking first in the country's traditional hot spring quality rankings. The town is built around the Yubatake — a vast wooden framework of channels through which the spring waters flow and cool before distribution — a steaming, sulfurous heart that has defined Kusatsu's identity and atmosphere since the town's founding. With a natural discharge rate of over 32,000 liters of hot water per minute, Kusatsu produces more thermal water than virtually any other hot spring in Japan, and its strongly acidic waters are renowned for their therapeutic properties.

Highlights

The Yubatake is the visual and spiritual center of Kusatsu, its wooden channels and steaming pools illuminated at night in a display that transforms the central plaza into something from another world. By day, the yellow-green tinge of the sulfurous water and the constant rising steam create an atmosphere that is simultaneously primal and cozy — the smell of sulfur that permeates the town is, for regular visitors, the very scent of relaxation and restoration. Surrounding the Yubatake, the town's streets are lined with ryokan inns, sake shops, confectionery stores, and souvenir stalls that collectively maintain a pleasantly old-fashioned onsen town character.

The waters of Kusatsu are so strongly acidic (pH around 2.0) that traditional wisdom holds they can "cure all ailments except lovesickness" — the acidity is believed to have powerful antibacterial and skin-renewing properties. Public bath facilities throughout the town allow day visitors to experience the waters without an overnight stay, and the outdoor foot baths at several locations along the main street offer a gentle introduction to Kusatsu's therapeutic offerings.

The Yumomi ceremony — a traditional method of cooling the ultra-hot spring water by rhythmically stirring it with large wooden paddles while singing traditional songs — is performed daily at the Netsu-no-Yu bathhouse, offering visitors a living demonstration of an ancient local tradition. This ceremony, which evolved as an alternative to adding cold water (which would dilute the water's medicinal properties), has become one of Kusatsu's most beloved cultural attractions.

Getting There & Tips

- From Nagano-hara-Kusatsu-guchi Station (JR Agatsuma Line from Takasaki), take a bus to Kusatsu Onsen Bus Terminal (approx. 25 minutes) - The Yumomi demonstration at Netsu-no-Yu charges approximately ¥600 per adult - Multiple public baths (Soto-yu) are free to use throughout the town - Book ryokan accommodations well in advance, especially for weekend and peak season stays - The town is walkable — most key attractions are within 15 minutes on foot from the Yubatake

Best Time to Visit

Kusatsu is a year-round destination, but winter (December to March) is arguably its finest season — the contrast of steaming hot spring waters against snow-covered rooftops and mountain slopes creates the quintessential Japanese onsen town atmosphere. Summer offers cool mountain temperatures when the lowlands swelter. The Kusatsu International Music Festival in summer and the Snow Festival in winter provide additional cultural programming.