Yumoto Onsen is a spectacular area to enjoy a hot-spring. Though not a hike in itself, several trails converge in the area and therefore have it listed on the hiking page. Especially if you've just hiked all day from Ryuzu Waterfall via Lake Yu, Lake Karikomi & Lake Kirikomi, through Kotoku or climbed Nantai Mountain or Shirane Mountain.
There are dozens of hot-spring inns north of Lake Yu and south of the source near the trail head to the Lake Karikomi & Lake Kirikomi hike.
Behind the hot-spring inns is the source >
There are wood planks to walk around the area as the area is very sludgey and wet.
Yumoto Onsen Temple in the background (Onsenji)
school children touch the hot water surfacing on a cool day
From near the trailhead to Lake Karikomi and Lake Kirikomi, there is a overview of the source and inns of Yumoto Onsen.