Shima Onsen

The road into Shima Onsen follows the Nakatsu River upstream through Gunma's Agatsuma district, climbing past forested ridgelines that close off the horizon on every side. The last few kilometers narrow further, and by the time you reach the village the mountains are so close around you that the sky above reads as a strip rather than a ceiling. Shima Onsen sits in that narrow floor, a small community built at the base of steep walls, and the Sekizenkan Honkan stands at its center, a wooden inn that opened in 1694 and is considered the oldest remaining hot spring inn in Japan. Miyazaki Hayao is said to have used it as a reference for the bathhouse in Spirited Away.

The spring water here is sulfurous and salt-enhanced, drawing from over forty separate sources across the village, with temperatures ranging from 43 to 82 degrees at the point of emergence. In the indoor baths, the water runs clear with a slight milky haze at higher temperatures, and the sulfur smell is present without being aggressive. It is the faintly eggy warmth of active geology, nothing chemical about it. Your skin comes out with a fine mineral coating that lasts, and the deep muscle warmth takes hold faster than you expect, especially in the Genroku-no-Yu baths at the Sekizenkan, which are themselves designated cultural assets of Gunma Prefecture.

The town's name carries a specific meaning. Shima translates as forty thousand, a reference to the traditional claim that the waters treat forty thousand different ailments. That claim sounds impossible and probably is, but the water is genuinely diverse, with different sources producing different mineral profiles across the three main districts of the village. Some baths are hotter, some more sulfurous, some with detectable salt content. You could spend two days moving between them and not repeat exactly.

The experience of Shima at night has a specific quality that the daytime does not match. When the last tour bus has left and the lanterns are lit along the riverside path, the mountain walls that crowd the valley turn black against the sky, and the only sounds are the river and the distant sound of bath water running through wooden pipes. The Sekizenkan's oldest wing has corridors that creak at every step, and the wooden bathtubs in the historic baths have the particular depth of color that comes from three centuries of mineral-stained water. It is not a polished place. That is precisely why it works.