The Okayama prefectural tourism association gives the colour at Okutsu-kei as late October to mid-November. The gorge runs about three kilometres near the village of Okutsu in the north of the prefecture, and a made-up path follows the water for most of that distance, so the whole thing can be walked rather than driven past.

The detail worth looking down for is underfoot. The riverbed here carries a run of potholes — round hollows drilled into solid rock by stones that the current has spun in the same spot for centuries. Individually they are common enough in mountain rivers. A concentration like this one is not, and it is part of why the gorge is named among the prefecture's set pieces rather than left as a local walk.

In the season the local guides run walks along the stream, with the geology and the history explained as you go. They fill, which tells you something about the crowds: visitors come from outside the prefecture for this gorge.

That has consequences for driving. Sections of the road become one-way on the busiest days, and on some days private cars are kept out altogether. It is twenty-five minutes from the Inno-sho interchange on the Chugoku expressway, but check what the Kagamino tourism bureau has posted before you set off — the restrictions change year to year.