Kawayu Onsen (川湯温泉)

Kawayu Onsen: The Acidic Heart of Akan-Mashu National Park

Kawayu Onsen is a destination where you can truly “smell” the earth’s vitality before you even see it. Located in eastern Hokkaido within the expansive Akan-Mashu National Park, this unique hot spring town is defined by its extreme acidity and its proximity to Mt. Iozan (Sulfur Mountain). The name “Kawayu” literally means “Hot Water River,” a tribute to the steaming mineral streams that flow through the town center, blanketing the streets in a mystical veil of white vapor. For those seeking the rawest form of Japanese thermal healing, Kawayu offers an experience that is both scientifically fascinating and spiritually rejuvenating.

Key Information

The Healing Waters: Extreme Acidity and “Peeling” Effects

The waters of Kawayu are famous for having a pH level as low as 1.4, which is comparable to the acidity of lemon juice or stomach acid. Scientifically, this level of acidity provides a powerful natural “peeling” effect, dissolving old skin cells and killing harmful bacteria. While the water may tingle or sting slightly if you have a scratch, it is renowned for curing chronic skin conditions that have failed to respond to modern medicine. The source of this power is Mt. Iozan, an active volcano just 2.5 km away, where rainwater is heated by underground magma and enriched with high concentrations of sulfur and iron before gushing forth into the Kawayu valley.

Top 5 Recommended Ryokans

• Kawayu Midoriya (Riverside Retreat): Famous for its large open-air baths built right along the banks of the hot spring river. It offers a perfect blend of modern comfort and natural immersion.
• Hotel Parkway (Rustic Charm): A favorite for travelers seeking a nostalgic, mountain-lodge atmosphere. It is known for its excellent locally-sourced venison and trout dinners.
• Oyado Kinkiyu (Traditional Heritage): A classic Japanese inn that focuses on high-quality thermal maintenance and traditional “Kaiseki” hospitality.
• Kawayu Kanko Hotel (Family-Friendly): One of the larger establishments in town, featuring extensive public areas and multiple tubs with varying mineral concentrations.
• Kussharo Genya Youth Guesthouse (Budget/Hostel): Located a short drive away, this is a top pick for international backpackers wanting to explore the lakes and onsens on a budget.

Must-Visit Public Baths (Soto-yu)

While Kawayu is a quiet town, its public facilities are exceptional. The Kawayu Eco Museum Center Footbath is free to the public and offers a relaxing place to soak your feet while looking out at the mossy forests. For a more traditional experience, many ryokans open their doors for day-use visitors for a fee of 500 to 1,500 yen. Don’t miss the Kawayu-jinja Shrine, which features a unique “Hand Bath” where you can wash your hands in 60°C geothermal water to pray for good health.

Walking Guide & Scenic Spots

The Tsutsujigahara Nature Trail is a 2.5 km path that connects the town to Mt. Iozan. This walk takes you through a forest of Sargent’s cherries and Labrador tea flowers that gradually gives way to a barren, lunar-like volcanic landscape. Once at Mt. Iozan, you can stand near steaming fumaroles and hear the roar of the earth. For a longer excursion, Kawayu serves as the perfect base for visiting Lake Mashu (known for its transparent blue water) and Lake Kussharo, where you can find “Sunayu”—a beach where you can dig your own hot spring bath in the sand.

Local Gastronomy & Souvenirs

Eastern Hokkaido is a paradise for food lovers. Try Mashu Pork, which is raised in the clean air of the highlands, or fresh Hime-masu (Kokanee Salmon) from the nearby lakes. For a relaxing break, head to Mori no Hall, a highly-rated cafe in front of the JR station famous for its seasonal fruit tarts. Souvenirs to look for include “Ainu Wood Carvings” and “Sulfur Bath Salts,” allowing you to take a piece of Kawayu’s healing power home with you.

Cultural & Historical Context

The town has a deep connection to the legend of Taiho Koki, one of the greatest Sumo wrestlers in history, who grew up in Kawayu. You can visit the Kawayu Sumo Museum to see his career highlights and learn about his love for the local springs. Historically, the area was first utilized by the Ainu people, who called the volcanic mountain “Atosanupuri” (Naked Mountain). Japanese development began in the Meiji era when sulfur mining became a major industry, eventually evolving into the world-class spa resort seen today.

Practical Travel Tips

Jewelry Warning: Because of the extreme acidity of the water, silver jewelry will turn black almost instantly. Always remove all rings and necklaces before entering the bath. Transportation: JR Kawayu Onsen Station is 3 km from the town center, so check the “Akan Bus” schedule in advance to coordinate with train arrivals. Cash: The town is quite rural; while hotels take cards, the local ramen shops and museums often require Japanese yen.

2025-2026 Latest Updates

In winter 2025-2026, the “Diamond Dust” Illumination event will take place on clear, cold nights in February, where powerful lights make frozen water vapor in the air sparkle like floating gems. Additionally, the Kawayu Bedrock Terrace has recently been updated with a new outdoor lounge area where visitors can enjoy natural steam heat even in sub-zero temperatures.

Safety & Manners

Due to the high mineral content and acidity, it is highly recommended to rinse your body with fresh water at the shower station before leaving the bath to avoid skin irritation. When walking near Mt. Iozan, stay strictly within the marked safety zones, as the steam can reach dangerous temperatures. Kawayu is a quiet residential town; please be mindful of noise levels during evening walks.