Tone Barrage
Connecting Saitama and Gunma's border, Tone Barrage was constructed in 1968 with the aim of supplying water for agriculture and for urban use in the Kennan and Tokyo areas.
There is an observation deck for the nature surrounding the garage where you can see salmon swimming up Tone River and so on.
Also, the upper reaches of the barrage are bustling with people enjoying windsurfing, jet skiing, and so on.