Shizuoka's official tourism guide gives the peak here as early to late November. The band is wide because the gorge is deep, and the upper reaches turn well before the water level does.

Sumatakyo is a valley on the Sumata, a tributary of the Oi, running about sixteen kilometres in all. What people come for sits at the far end of the hot spring village: a suspension footbridge over a pool of green water. The bridge is the picture, but the walk around it is the better use of the day — the Sumatakyo Promenade Course takes in the bridge and returns in roughly ninety minutes. The hot spring at the end of it is an alkaline simple sulphur water rising from the foot of the Southern Alps.

Getting there is the constraint. The main route is prefectural road 77 from Senzu station on the Oigawa Railway, about fifteen kilometres of narrow road along cliffs and through tight curves. Large buses struggle with it. Passing places are limited, so leave time and expect to give way.

Local buses do run from Senzu, though not often, and the ride is worth taking for its own sake because the river stays in view from the window. If you are driving, go early. The road is the bottleneck rather than the parking, and it does not improve once the day's traffic is on it.