Lake Kussharo

Kussharo is the largest caldera lake in Japan, about twenty kilometres across, with a wooded island in the middle that is itself a volcanic cone. Geothermal water rises through the lake bed and the beaches along the shore, and at Sunayu the practical consequence is that you can dig a hole in the sand with your hands and it fills with hot water - people bring spades and make their own baths a metre from the cold lake. That same geothermal input keeps sections of the lake ice-free through winter, which is why several hundred whooper swans overwinter here rather than continuing south, standing in the steaming shallows. Free open-air hot spring baths sit directly on the shoreline at Kotan and Wakoto, some with no walls at all. The lake is acidic from volcanic input and supports little fish life.

What you actually see

• Dig-your-own baths - hot water rising through the beach sand at Sunayu.
• Wintering swans - whoopers on the geothermally warmed open water.
• Shoreline rotenburo - free open-air baths at the lake edge, some unwalled.
• The largest caldera lake - about twenty kilometres across with a volcanic island.

When to go

June to October for the shore; December to March for the swans. A day.

Honest expectations

The open-air baths are mixed and largely unscreened - some visitors find that uncomfortable. Public transport around the lake is very limited. The water is acidic and swimming is unappealing. Winter roads need care and snow tyres.

Nearby

Lake Mashu is east; Kawayu Onsen is between them.