Marukoma Onsen Ryokan

Marukoma has stood alone on the northwest shore of Lake Shikotsu since 1915, and before there was a road, guests crossed the lake by boat. The bath people come for is down a corridor from the main bathhouse. It's a rock pool walled off from the lake by boulders, and the spring rises through the gravel under your feet.

The inn says only about twenty baths in Japan bubble up from directly beneath the bather like this. Because the pool sits at lake level, its depth follows Shikotsu up and down through the year. The water is as clear as the lake. It's a neutral salty spring that comes off the volcano Eniwa-dake at 54°C, and the sauna's cold plunge runs on Shikotsu lake water.

Day bathing runs Friday to Sunday from ten until two, which suits a slow morning before an afternoon flight out of New Chitose. Better still, stay the night and get into the lake bath at dawn, when the baths reopen for guests from four.