Matsukawa Onsen is one of Hachimantai's classic mountain bath stops, tucked in the Matsukawa Gorge below the higher plateau roads. The water is sulfurous and pale, the setting is forested, and several lodges open their baths to day visitors.
It works best as the slow half of a Hachimantai day. Hike or ski first, then come here for a soak before heading back down toward the towns and stations.