Niyodo River Yasui Valley is a valley created by the Yasui River, a tributary of the Niyodo River, located in Niyodogawa Town, Agawa District, Kochi Prefecture. It is said to be a sacred place representing "Niyodo Blue", and the color of its highly transparent water, which shines from emerald green to cobalt blue, is truly breathtakingly beautiful. Dotted with huge rocks and oddly shaped rocks, the clear stream that flows through them, and the scenery woven by the abundant nature are so fantastical that it could be called a hidden place in Japan, and many photographers and tourists visit.

In particular, "Suishobuchi", known as a highlight of the valley, is a place where the crystal clear water, as its name suggests, shows off the most beautiful Niyodo blue. There are plenty of other sights to see, including the impressive waterfalls Hiryu Falls, Shoryu Falls, Seryu Falls, and Mikaeri Falls, as well as the mysterious emerald green Senjinkyo Gorge, Yasui River Sabo Dam, and Seriwari Cave. There are walking paths so you can enjoy a leisurely stroll while listening to the sound of the clear stream.

Yasui Valley offers a variety of activities, including hiking, camping, and playing in the river.

If you want to enjoy camping, canoeing, or SUP, popular spots downstream of Yasui Valley include the Niyodo River Outdoor Center and Miyazaki Riverside Campsite.