Koshibuko Onsen

Koshibuko Onsen is a sulfurous thermal spring in Nagano Prefecture, its volcanic waters carrying the characteristic hydrogen sulfide compounds that give the spring its distinctive aroma and the therapeutic potency that has made sulfurous springs among the most medically respected in Japanese balneological tradition for their antibacterial, circulatory, and skin-cleansing effects. Nagano Prefecture's volcanic highlands produce sulfurous springs of excellent quality across multiple mountain systems, from the Joshinetsu to the Kiso and Ina regions, and Koshibuko's sulfurous character connects it to this broader volcanic spring tradition of Japan's most thermally active inland prefecture. This spring offers the assertive mineral experience of the volcanic earth in the concentrated form characteristic of Nagano's most potent thermal resources.