I went to "Borou NOGUCHI Noboribetsu" in Noboribetsu Onsen.
Noboribetsu has a large amount of hot water, so all 40 rooms have observation baths with natural hot spring water.
It is a milky white sulfur spring, and has a hot spring feel similar to that of The Onsen.
The concept is to be a "private space for adults," so children under elementary school age are not accommodated. Please be careful if you are bringing children.
【Official Site】
https://www.bourou.com/
Noguchi Kanko Group
https://www.noguchi-g.com/