Kashi Onsen (甲子温泉)

Introduction: The Ancient Hidden Spring of the High Mountains

High in the mountains of Nishigo Village, at the very source of the Abukuma River, lies Kashi Onsen (甲子温泉). Discovered over 600 years ago in the era of “Kashi” (the first year of the 60-year cycle), this hot spring has long been a “secret bath” for mountain ascetics and travelers traversing the Kashi Pass. Surrounded by the dense forests of the Nikko National Park, Kashi Onsen offers an atmosphere of profound seclusion. The crown jewel of this area is the Daikokuya inn, which has stood as a solitary guardian of the spring for centuries. For the international traveler, Kashi is the ultimate destination for “Shinrin-yoku” (forest bathing) combined with authentic mineral therapy. Here, the modern world feels distant, replaced by the sound of waterfalls and the steam of the ancient “Oiwaburo” (Big Rock Bath)—a massive tub carved directly into the bedrock over a natural spring source. It is a place of spiritual and physical reset, where the water is as pure as the mountain air.[2, 5]

Key Information Table

The Healing Waters: The Sacred “Oiwaburo”

Kashi Onsen is famous for its Oiwaburo, a historic communal bath that is 5 meters wide and 15 meters long, carved directly into the mountain rock.[5]

Balneological Properties: The water is a Simple Thermal Spring, meaning it has a balanced mineral profile that is low in irritation but high in therapeutic heat. From a scientific perspective, these “Simple Springs” are prized for their versatility; they are often used in medical balneology to treat convalescence and fatigue without overstretching the body’s regulatory systems.[2]
The water at Daikokuya flows directly from the floor of the pool, meaning you are soaking in water that has never touched the air—preserving its raw volcanic energy. Note: The Oiwaburo is traditionally a mixed-gender bath (Konyoku), but it has dedicated hours for women only (5:00 AM – 7:00 AM and 7:00 PM – 9:00 PM) to ensure comfort for all travelers.[5]

Top Recommended Stay

• Ryokan Daikokuya (旅館 大黒屋): The soul of Kashi Onsen. This historic lodge provides a traditional Japanese experience with tatami rooms and meals featuring mountain vegetables and river trout. It is a member of the “Japan Association of Secluded Hot Springs” (Nihon Hitou o Mamoru Kai). Their staff are accustomed to foreign guests seeking a quiet, meditative stay.

Must-Visit Neighborhood Spots

Shirakawa Daruma Market (Nearby): If visiting in February, don’t miss this massive cultural festival in Shirakawa City where thousands of good-luck daruma dolls are sold.

Kashi Bridge: A spectacular red bridge spanning the valley, offering one of the most iconic photo spots in the Tohoku highlands, especially during the autumn foliage peak in late October.

Safety & Manners

Mixed Bathing Etiquette: For the Oiwaburo, towels can be used for modesty during mixed hours, but always check the inn’s specific rules upon arrival.

Wildlife: As Kashi is deep in the mountains, be aware of wildlife such as macaques and occasionally kamoshika (Japanese serow). Keep a respectful distance.

Winter Warning: The road to Kashi (National Route 289) is steep and experiences heavy snowfall. 4WD and studless tires are mandatory from December to April. Rental car companies at Shin-Shirakawa Station provide these as standard, but confirm during booking.