Yunose Onsen (湯の瀬温泉)

Introduction: The Pool of Serenity—Japan’s Giant Source-Fed Secret

Deep in the silent valley of the Iragawa River, tucked away from the coastal winds of Tsuruoka, lies Yunose Onsen (湯の瀬温泉). This destination is home to a single, legendary inn: Yunose Ryokan. For the international traveler, Yunose is the ultimate architectural and geothermal curiosity. It features a “Pool-Sized” Open-Air Bath—one of the largest in Northern Japan—holding a massive volume of 100% pure, unheated mineral water.[11, 12, 13] Combining the rustic charm of a carp-breeding history with the sophisticated skin-beautifying chemistry of a high-alkaline spring, Yunose offers a “hidden” experience that satisfies the modern craving for authentic, sustainable wellness.[12, 14]

Key Information Table

The Healing Waters: The Science of pH 9.2

Yunose Onsen’s reputation among balneologists is built on its Voluminous Purity.
800 Liters Per Minute: This staggering flow rate allows the inn to fill a 23-meter long bath with fresh water every few hours without ever recycling (circulating) a single drop. It is 100% Gensen Kakenagashi.[12, 14]
The Peel Effect: With a pH of 9.2, the water acts as a mild alkaline peeling agent. It softens the outer layer of the skin (keratin) and emulsifies sebum, providing a “Sube-Sube” (slippery) sensation that leaves you glowing after the bath.
Standing & Walking Bath: The outdoor pool is 1.2 meters deep. This depth provides hydrostatic pressure that aids in blood circulation and allows for Underwater Walking, making it a premier spot for muscle and joint recovery.

Top Stays & Strategic Bases

• Yunose Ryokan (湯の瀬旅館): The only way to stay. A traditional inn featuring spacious tatami rooms (some with private toilets) and a 100-year-old hospitality style. Famous for its “home-cooked” seafood feasts.
• Bankokuya (Atsumi Onsen): A 25-min drive away. A 5-star historic ryokan for those who prefer high-end luxury after a day visit to Yunose.
• Suiden Terrasse: A 30-min drive away in central Tsuruoka. A modern architectural masterpiece built in a rice paddy, perfect for younger design-conscious travelers.
• Haguro Sanrokusha (Shukubo): Located 40 minutes away. Stay in a Buddhist temple lodge to combine the “Pool Onsen” experience with early morning prayers.
• Super Hotel Yamagata-Tsuruoka: For budget-conscious business travelers, this modern hotel is just a 20-minute drive from the Iragawa turn-off.

Must-Experience: The “Pool” and Mixed Bathing Etiquette

The centerpiece is the Dai-Rotenburo (Great Outdoor Bath). At 23m x 13m, it feels like a swimming pool.
Mixed Bathing (Kon-yoku): This bath is mixed-gender. To ensure comfort for international visitors:
Yuami-gi (Bathing Wear): The ryokan provides dedicated bathing clothes for women to rent.
Towel Policy: Because the water volume is so high and constantly overflowing, you are permitted to wrap yourself in a clean towel while in the water.
Koi Pond: Don’t miss the lobby pond. The inn started as a Nishikigoi Carp farm; the founder discovered the spring by noticing the carp survived the blizzard only in one specific section of the river where warm water bubbled up.

Local Gastronomy: The UNESCO City Bounty

Tsuruoka is a UNESCO Creative City of Gastronomy.
Seafood Focus: The ryokan specializes in Shonai-hama cuisine—specifically crab and red sea bream served in “Ofukuro-no-aji” (mother’s home-cooking) style.
Vegan & Vegetarian Survival:
“Do You Know?” (Vegetime Restaurant): Located 35 mins away in Haguro. They serve 30-40 types of heirloom vegetables in a “quasi-vegetable” lunch (2,200 JPY). A pilgrimage site for vegans.
Soto-Zen Temple Food: Nearby Zenpoji and Miyata-bou offer authentic Buddhist vegan courses using local mushrooms and sesame tofu.

Historical & Cultural Context

The story of Yunose is one of Persistence. After the carp discovery, experts told the founder that further drilling was a waste of time. He ignored them, drilling to 1,050 meters depth. On Christmas Day 1991, he struck the 48°C source that flows today. This “Christmas Miracle” transformed a mulberry field into a sanctuary of health.

Practical Travel Tips

• Cash Only: Unlike larger resorts, Yunose Ryokan does not accept credit cards. Ensure you withdraw JPY at the 7-Eleven near Atsumi Onsen before heading into the valley.
• Tattoo Policy: Generally accommodating due to the private nature of the inn. However, use the large outdoor bath during quiet hours (e.g., late night or early morning) as a courtesy.
• Language Barrier: Signage is limited to Japanese. Use the “Voice Translator” app; the staff are incredibly friendly and used to non-verbal “Omotenashi.”[10, 14]

2025-2026 Latest Updates

Kamo Aquarium (Jellyfish Dream Yakata): The world-famous aquarium (30 mins away) will be closed for renovations from November 2025 to March 2026. Plan your visit for Spring 2026 to see the grand reopening.[17]
Pagoda Light-up (Summer 2026): Following the “Great Renovation” of the National Treasure Five-Storied Pagoda at Mt. Haguro, night-time illuminations are scheduled to return in the summer of 2026.[15, 16]

Safety & Manners

Walking in the Tub: Because the floor of the large pool is natural stone, it can be slippery. Walk slowly.
The “Salt Stinging”: While simple alkaline water is gentle, if you visit the nearby salty springs of Yunohama earlier, rinse your skin before entering Yunose to avoid chemical irritation.
Winter Roads: The road along the Iragawa River is prone to icy patches. Use Snow Tires or take a taxi from Tsuruoka Station.