Sendatsu-gawa-no-yu is a wild hot spring located in the Nyuto Onsen area of Senboku City, Akita Prefecture, near Ipponmatsu Onsen Tatsuko-no-yu. It's known as an extremely difficult-to-find hidden hot spring, so secretive that even locals are often unaware of its existence. This mystical wild hot spring is surrounded by untouched nature in every direction. The hot spring water bubbles up from the bottom and can be scalding hot in some areas, requiring bathers to find their own comfortable temperature spots. The bottom is filled with accumulated mud that has a silk-like soft texture, enjoyed as beauty mud. The area has concentrated hydrogen sulfide gas and is known as a dangerous location, requiring extreme caution.