Azumaya has two locations, a fancier ryokan and a more affordable minshuku about 100m from each other. We stayed in the simple minshuku on our visit here but were able to use the baths in both facilities. Both facilities were very quiet when we were there. The little village around Yunomine Onsen and Tsubo-yu has some very busy days but outside of those times it's dead quiet and that is totally awesome. It was also interesting to see how many international tourists now come to the area. In our minshuku there was two Australians and a German, if you include me and my daughter there were more non-Japanese than Japanese guests!
The water is the absolutely perfect at Yunomine Onsen. No complains ever for this spring. It's 100% quality. In the minshuku the bath was small and well used but had a nice window. The ryokan's bath was much larger but also had that old wooden feel to it. The rotenburo was newer and had a great garden around it. I would highly recommend both lodgings if your looking to spend the night and using the day use option for the ryokan's bath if Tsubo-yu is booked out.