Kotan Onsen (コタン温泉)

Introduction: Soaking at the Water’s Edge with the Majestic Whooper Swans

On the rocky northern shores of Lake Kussharo, where the ancient volcanic earth meets the largest caldera lake in Japan, lies Kotan Onsen (コタン温泉). This is not a commercial resort, but a breathtaking, community-maintained outdoor bath that has become a bucket-list destination for photographers and nature lovers worldwide. The name “Kotan” comes from the Ainu word for “village” or “settlement,” reflecting the deep indigenous roots of the area. For the international traveler, Kotan Onsen offers a surreal, ethereal experience: soaking in natural mineral waters that are separated from the icy lake only by a row of stones. In winter, this experience reaches its peak as hundreds of migratory Whooper Swans float just inches away from the bath, creating a scene of peace and natural harmony that feels like a living painting. It is the ultimate expression of Hokkaido’s wild beauty and the welcoming spirit of its remote communities.

Key Information Table

The Healing Waters: Volcanic Purity at Lake Level

The water at Kotan Onsen is a high-quality Sodium-Bicarbonate Spring that flows directly from the earth at around 40-42°C. It is 100% “Gensen Kakenagashi,” used exactly as it emerges with no filtration or recycling. The water is clear and carries a very mild, pleasant mineral scent. Bicarbonate ions are known as “nature’s soap,” gently exfoliating the skin and leaving it feeling incredibly silky. The most unique feature is the Rotenburo’s location: the tub is built at the same level as the lake surface. As you submerge, your line of sight aligns with the vast blue horizon of Lake Kussharo, creating an “infinity pool” effect that connects you directly to the water and the mountains beyond.

Top Recommended Bases & Logistics

Since Kotan Onsen is a public outdoor bath with no lodging, travelers stay in the small hamlet surrounding it.

• Guesthouse Kotan (Ainu-ya): Located just steps from the bath. This cozy guesthouse is famous for its Ainu-inspired decor and hearty local meals. It is the best place to stay for those who want to experience a “Midnight Soak” or catch the sunrise over the lake.
• Marukibune: A rustic, traditional inn nearby that also features its own private onsen and a restaurant serving local venison and mountain vegetables.
• Wagoto Peninsula Campground: A 10-minute drive away. Many camper-van travelers use Kotan as their primary morning bath before exploring the national park.

Must-Visit Neighborhood Spots: Swans and Ainu Culture

Whooper Swans (Winter Only): From December to March, the geothermal heat keeps the water near Kotan from freezing, attracting hundreds of swans. They are accustomed to humans and will often swim right up to the edge of the onsen tub.
Kotan Ainu Museum: A small but profound museum in the village center that showcases the history, tools, and spiritual beliefs of the local Ainu community.
Bihoro Pass: A 20-minute drive that offers a panoramic view of the entire lake and the central “Nakajima” island. It is considered the most beautiful viewpoint in eastern Hokkaido.

Local Gastronomy: The Bounty of the Basin

The food in the Kotan area is simple and deeply connected to the forest and lake.
Wakasagi (Lake Smelt): Try the smelt tempura at the local inns; the fish are caught directly from the clear waters of Lake Kussharo.
Mashu Soba: The nearby Teshikaga area produces high-quality buckwheat.
Vegetarian/Vegan Survival:
For Vegans: Teshikaga town (15 mins away) has a great Michi-no-Eki with fresh local corn, potatoes, and pumpkins. In the village, “Marukibune” can sometimes prepare vegetable-only dishes if notified in advance. We recommend ordering “Zaru Soba” and specifying “Salt and Wasabi” to avoid the fish dashi. Pro Tip: Buy the local “Mashu Milk” yogurt if you are a vegetarian—it is world-class.

Cultural & Historical Context

Kotan Onsen has been used by the Ainu people for centuries as a place of purification and physical healing. They viewed the hot water as a gift from the “Kamuy” (gods) of the volcano. In the late 20th century, the local residents built the current stone tubs and changing rooms to preserve the spring for everyone. Today, it remains a symbol of “Common Land,” where locals and travelers from across the globe meet as equals in the water, following the ancient rules of respect and quietude.

Practical Travel Tips for International Visitors

• Tattoo Policy: As a wild, outdoor public bath with no staff, there are no restrictions on tattoos. It is a haven for international travelers with extensive ink.
• Bathing Style: Kotan is a mixed-gender bath (Konyoku), but it is very well-managed. There is a simple stone partition in the water between the men’s and women’s sides. **Wearing swimwear is permitted and highly encouraged** for international visitors and female bathers to ensure comfort. Separate wooden changing rooms are provided.
• Winter Gear: The area around the bath can be icy and extremely slippery in winter. Wear boots with good grip. The temperature outside can be -15°C, while the water is 42°C—the “shock” is exhilarating but requires a healthy heart.
• Cash Only: While the bath is free, there is a donation box for maintenance. Please bring 100-yen or 500-yen coins to contribute to the local community that keeps the bath clean.

2025-2026 Latest Updates

In 2025, the village completed a renovation of the wooden changing rooms, adding solar-powered lighting for safer nighttime use. For the 2026 winter season, a “Swan Etiquette Guide” in English will be available at the trailhead, reminding visitors not to feed the birds or use flash photography too close to the water.

Safety & Manners

In the onsen, do not use soap or shampoo—the runoff goes directly into Lake Kussharo. Keep the water pure. Always rinse your feet before entering the tub to remove sand. Respect the “Quiet Hour”—early morning and sunset are peak times for wildlife and photographers; avoid loud talking during these times. Finally, be “Bear Aware”—while rare near the shore, the surrounding forests are bear territory; do not leave any food trash behind.