The valley of the Yokoyu and Yomase rivers holds nine distinct hot springs, spread along the hillsides of Yamanouchi in Nagano Prefecture. Together they form a single resort township — Yudanaka Shibu Onsen — yet each retains its own character, its own particular water. At Kakuma, the natural radon concentration is among the highest in the country. At Shibu itself, the baths carry multiple mineral profiles, shifting from one bathhouse to the next in ways that reward the patient guest rather than the passing visitor. There are said to be more communal bathing halls here than anywhere in Japan save Beppu. That is not a boast so much as a fact about how the place was built — for repeated use, for people who came to stay.

The development that began in 1891 left certain traces still visible in the fabric of the streets. Shibu retains the density of a traditional bath town, its lanes close enough that the sound of water never quite leaves you. The township as a whole runs to roughly a hundred inns and hotels, yet the atmosphere tilts toward the older idea of *tōji* — prolonged bathing as a practice, not a single evening's indulgence. Near Shin-Yudanaka, a morning market and a row of willows mark the space beside the station.

To stay for several nights here is to fall into a different kind of attention. You begin to notice which bath opens earliest, how the water at one source differs from another a short walk away. National Route 292 connects the area westward into Gunma Prefecture, and the station at Yudanaka anchors the valley to the wider world — but neither road nor rail quite explains why people return. The waters do that quietly, on their own terms.