This was, hands down, the BEST part of our trip to Japan.
We chose the room with open air private bath for our stay.
Traveling to the location was a bit difficult. Make sure to know the shuttle times from Minobu to Nishiyama Onsen Keiunkan. The reason for this is that we arrived at 1400 and the shuttle had left during 1300-1400. The next shuttle arrived at 1800. We had to spend a lot of money on a taxi to get to the ryokan.
Arriving at the onsen we met the faculty of the onsen outside who greeted us and directed us to the room immediately. Thereupon we were informed by a member whot told us about all the amenities, procedures, and details of the ryokan.
After that we were left to explore and relax at our own leisure.
I do not have enough characters left in this review to gush about how amazing this location was. It was definitely a once in a lifetime experience, and that the private open air bath is absolutely worth it.
I would LOVE to do this again with some friends.