Iwa-no-yu is one of the five public onsen that is run by Yuzawa town and is probably the least well known of the lot due to its location. The others are either in the town or along one of the main roads. Iwa-no-yu is worth seeking out though as it is a quaint little onsen liked by locals, with a real rustic feel to it.
The onsen is about 10 minutes drive from Echigo-Yuzawa Station, out past Iwappara. It is right next to Yuzawa Fishing Park, both of which are situated right on the banks of the river. (A swimming hole popular with the local children is just down stream from here as well.) The entrance ticket is cheap; just 400 yen for adults or 200 yen for children, which you drop into the vending machine. There is a small tatami resting area when you go in which is decorated with lots of interesting objects. There is a stuffed bear and a stuffed kamoshika deer as well as several traditional tools, and winter wear made of rice stalks.
The baths themselves are quite small, though there is easily enough room for a dozen people and we had the place to ourselves when we were there. The facility takes its name from the stone which paves the bathroom and from which the baths are made. There are large windows looking out on to the river and up onto the heavily wooded mountain on the other side. With the windows open you hear the sound of the river flowing past, and with the view of the trees as well, it is incredibly relaxing. It is a bit of a change to have a soak in an onsen that is so close to nature, as often you find yourself surrounded by fences out the back of a hotel. Part of the charm of Iwa-no-yu is that it is a little off the beaten track and isolated.
It is not far from Iwappara, Yuzawa Park and Nakazato Ski Resorts so we will definitely be heading back in winter to enjoy a long, hot soak after a day on the slopes. It is a great option for those looking for an authentic onsen experience away from larger spa complexes.