A bit out-of-the-way, but the tranquility might be exactly what you want in an onsen town.
Kinosaki Onsen is located near the Sea of Japan, in Hyogo Prefecture, but on the opposite side, away from Kobe. The onsen has been given 2 stars by Michelin’s Green Guide.
(English, Japanese, Chinese and Korean language site)
The main town is dominated by ryokans and bathing facilities, so it is pretty normal to see people watching around in yukata (yukata is a light cotton kimono) with towels and toiletries with them.
Every ryokan should provide you with a yukata to walk around in, but there are also rental ones available.
Wearing hotel yukata is not as difficult as wearing a yukata for a festival or a kimono for an event. You can put it on rather easily by yourself.
There are 7 public baths in the area, and they are free to use for the guests of the town’s ryokans
A guide to the different bathhouses in the downtown area is here:
Another attraction in the area is Kinosaki Marine World.
Japanese people really enjoy their aquariums and they are usually pretty entertaining. This might be a good side trip if you are traveling with children or like aquatic life.
Entrance fee: 2,470 yen for adults; 1,230 yen for elementary to junior high kids, 620 yen for 3 yrs old+