Kusatsu Onsen (Yubatake Hot Spring Field, Yumomi Performance & Sainokawara)

Category: Natural Geothermal Onsen & Cultural Performance | Location: Kusatsu, Agatsuma-gun, Gunma 377-1711 (Kusatsu Onsen Bus Terminal)

Voted uninterruptedly as Japan’s #1 Onsen by travel industry professionals for over two decades, Kusatsu Onsen in Gunma Prefecture stands as the undisputed king of Japanese geothermal hot springs. Perched at 1,200 meters above sea level in the volcanic highlands, Kusatsu boasts Japan’s highest natural spring water output, gushing an astounding 32,300 liters per minute. Its intensely acidic waters (pH ~2.1) possess peerless natural antibacterial properties, famously celebrated in Japanese proverb as "curing every affliction known to man, except lovesickness." The town’s pulsating heart is the monumental "Yubatake" ("Hot Water Field"), an iconic terraced network of cedar wood conduits through which 55°C thermal waters cascade to cool naturally before being piped into local ryokans, simultaneously harvesting pure sulfur "Yunohana" mineral crystals. Directly adjacent is the historic Netsu-no-Yu theater, home to the hypnotic "Yumomi" performance—a centuries-old ritual where women in traditional kimonos stir boiling thermal pools using 1.8-meter pine planks while chanting the rhythmic folk melody "Kusatsu Bushi" to lower water temperatures without dilution. On the western edge lies Sainokawara Park and the breathtaking Sainokawara Outdoor Bath—one of the largest open-air hot-spring pools in Japan covering 500 square meters immersed within a steaming natural volcanic ravine. Reachable via the direct JR Limited Express Kusatsu-Shima from Tokyo’s Ueno Station to Naganohara-Kusatsuguchi, followed by a scenic 25-minute connecting bus.