Yubara Onsen in the north mountains of Okayama Prefecture is famous for open-air mixed baths right below a dam. They are called suna-yu ('sand bath') because the sand blows up with hot waters springing out from the riverbed. There are three bath pools are formed with natural rocks, and you can relaxingly soak in the hot spring while enjoying views of the towering dam, a distant suspension bridge and surrounding nature, free of charge.
If you are timid, there is a bathhouse across the river, equipped with sauna and jacuzzi. There are many interesting museums in this resort, including the one explaining hot springs and others displaying spinning tops and rare freshwater creatures such as Japanese giant salamander. Downstream the river, there are four other onsen towns.
Airport/Sta.Okayama Airport (about 50.5km) Google Transit