Miyauchi Onsen (宮内温泉)

Introduction: The Ancient Edo-Era Sanctuary of the Kariba Mountains

Deep within the mist-shrouded valleys of Shimamaki Village, where the Kariba mountain range meets the raw energy of the Sea of Japan, lies Miyauchi Onsen (宮内温泉). This is one of Hokkaido’s most historically significant “one-inn” lodges, with roots stretching back to the late Edo period (mid-19th century). Known as a “Hitou” (hidden hot spring) of the highest order, Miyauchi Onsen has served as a sanctuary for explorers, foresters, and those seeking the profound healing powers of its massive, self-springing tubs. For the international traveler, Miyauchi Onsen represents the “Soul of the Frontier.” It is a place where you can soak in mineral-rich waters that have flowed for over 160 years, breathe in the air of Japan’s northernmost beech forests, and experience the quiet, unpolished hospitality of a family that has guarded this spring for generations. If you seek a destination where time is measured by the rustle of the leaves and the rising steam of the earth, Miyauchi is your essential northern retreat.

Key Information Table

The Healing Waters: A Century of Geothermal Abundance

The water at Miyauchi Onsen is geologically unique in the Oshima Peninsula. It is a powerful Sodium-Chloride / Bicarbonate / Sulfate Spring.
The Volume: The spring flows naturally from a deep underground vein at a staggering volume, requiring no pumps or artificial heating.
The Sensation: The water is crystal clear and odorless, with a notably “thick” and slippery texture—the classic “Bijin-no-yu” (Beauty Water) effect. The bicarbonate ions gently exfoliate the skin, while the salt and sulfate content provide a deep, internal warmth that penetrates the body core—a vital quality in Shimamaki, where the sea winds are legendary. The facility features a massive indoor bath built with traditional timber and an outdoor Rotenburo that looks directly into the virgin forest. To soak here is to feel the weight of history and the raw energy of the Kariba volcanoes in every drop.

Top Recommended Stay: Miyauchi Onsen Ryokan

• Miyauchi Onsen Ryokan (宮内温泉旅館): The only place to stay in this hidden valley. It is a traditional Japanese inn that prioritizes mineral purity and silence. The rooms are simple tatami spaces with views of the mountain stream. The building itself is a “living museum” of Showa and Meiji era architecture. The highlight is the dinner service, featuring world-class Shimamaki Scallops and wild mountain vegetables (sansai). Note: Guest rooms do not have private bathrooms or high-speed Wi-Fi; the experience is about returning to the basics of Japanese mountain life.

Must-Visit Neighborhood Spots: Waterfalls and Beech Forests

Garo-no-taki (Garo Falls): A short drive away, this is one of the “Top 100 Waterfalls in Japan.” Known as the “King of Hokkaido Waterfalls,” it is a massive, broad cascade surrounded by primeval forest.
Kariba-yama (Mt. Kariba): For experienced hikers, the trails near the onsen lead toward the summit of this iconic peak, offering panoramic views of both the Sea of Japan and the Pacific.
Shimamaki Primeval Beech Forest: Japan’s largest stand of natural beech trees. Walking through these “ghostly” white woods is a world-class forest bathing (Shinrin-yoku) experience.

Local Gastronomy: The Giant Scallops of Uchiura Bay

Shimamaki is legendary for its Scallops (Hotate) and Abalone (Awabi).
Shimamaki Scallop Steak: The cold, nutrient-rich currents of the Sea of Japan produce massive scallops. They are often served grilled with local butter at the ryokan.
Wild Sansai (Mountain Vegetables): In spring, the valley provides “Urui” and “Fuki” (butterbur) that are served as crispy tempura.
Vegetarian/Vegan Survival: Being a remote fishing and mountain village, plant-based options are limited.
For Vegans: We recommend bringing your own protein and snacks from Hakodate or Otaru. At the onsen lodge, you can request “Mountain Vegetable Soba”—specify “Katsuo-dashi nuki” (No fish dashi). The local “Shimamaki Potatoes” are world-class—simply steamed with salt, they are a perfect 100% vegan snack.

Cultural & Historical Context

Miyauchi Onsen was discovered by a pioneer named Miyauchi in the mid-19th century, who noticed that injured deer and brown bears would congregate at the steaming seepage near the river. For over 160 years, it has served as a “Toji” (healing clinic) for the local community. The lodge stands as a symbol of rural Hokkaido’s resilience—a place that has survived extreme winters and economic shifts by remaining true to its mineral roots. The name “泊” (Tomari) refers to the area’s history as a vital stopover point for travelers crossing the rugged coastline.

Practical Travel Tips for International Visitors

• Tattoo Policy: As a secluded and traditional “Hitou,” Miyauchi is generally very tolerant of tattoos. The owners are used to independent travelers from around the world who seek hidden springs. Full ink pieces are rarely an issue here if the guest is respectful.
• Connectivity: Zero mobile signal inside the valley. There is no Wi-Fi in the guest rooms. Prepare for an “offline” experience. Download your Mapcode and offline maps before leaving the town center.
• Cash Only: This is a traditional lodge in the mountains. Credit cards are not accepted. Bring sufficient cash for your room and bathing fees. The nearest ATM is 20km away in central Shimamaki.
• Access: A rental car is highly recommended. The road to the onsen is narrow and winding. Winter access: The road is plowed but can be extremely snowy; expert winter driving skills and a 4WD vehicle are required.

2025-2026 Latest Updates

In 2025, Miyauchi Onsen introduced a “Heritage Trekking Stay”, providing guests with binoculars and maps for the private forest trails behind the lodge. For the 2026 season, the lodge is planning to refurbish its historic “Source Well” viewing area to allow guests to see the water surging from the earth before it reaches the tubs.

Safety & Manners

In the onsen, always sit on the provided stools while washing and do not splash water. Because the water is high in bicarbonate and slippery, walk slowly to avoid falls. Be “Bear Aware”—carry a bear bell if you are walking on the trails near the lodge. Finally, respect the quiet; many guests stay here for the silence of the mountains, so keep conversations in the communal baths to a respectful whisper.