Nikkō Yumoto Onsen, onsen resort on Lake Yunoko in Nikkō, Tochigi, Japan

Nikkō Yumoto Onsen is a sulfur spring resort in the mountain region around Nikko, fed by multiple hot springs. The area consists of several traditional inns and public bathhouses spread across different elevations, with water that has a yellowish color and a distinctive sulfur smell.

The hot springs were discovered in 788 by the monk Shōdō, founder of Shihonryū-ji, not in the Edo period. Until the early Shōwa era the severe winter cold meant the baths operated mainly as a summer cure. The Edo-period text Nikko Sanshi records nine large bathhouses on the flat ground by Lake Yunoko, managed by Nikko town officials who carried supplies in on their backs.

The Yumoto Onsen area is a traditional hot spring resort where visitors can observe how thermal waters have been used for centuries. The small inns and public bathhouses reflect a culture where soaking in hot springs is not just relaxation but part of daily life.

Visitors should know the area is hilly and good shoes are needed for exploring. Many of the inns have small outdoor baths open to guests, while some public baths can also be used by day visitors without staying overnight.

The springs emerge in the Yunodaira marsh at the edge of the resort, each source covered by a protective roof. Their water is piped not only to Yumoto's inns but also to Kōdō Onsen nearby and as far as Chūzenji Onsen. Source temperatures range from 49.3 to 78.9 °C, and the water is a weakly acidic hydrogen sulfide sulfur spring with a pH of 6.33 to 6.6.