The Nakatsugawa tourism association gives the colour at Tsukechi-kyo as late October to early November. The gorge lies in the mountains in the north of Nakatsugawa city, on a tributary that eventually reaches the Kiso river, and it is part of a Gifu prefectural natural park.

What makes it unusual is the water. The Tsukechi is known locally as the blue river, and the colour is not a trick of a summer sky: it holds through autumn, so the reds and yellows on the banks sit against blue-green rather than against grey. Photographers come for exactly that contrast, and they gather in the same three places every year. Hondani bridge and Semeru bridge both cross high enough to look straight down into the water. The third is the ground around Fudo falls, where the river drops through rock.

The walk between them is short and the paths are made up rather than wild, so this is an easy stop rather than a hike. An hour and a half covers the bridges and the falls at a slow pace.

The approach road is narrow and carries two-way traffic in the season, with few places to pull over. Early morning is better for both the parking and the water, which reads bluest before the sun is high. Nakatsugawa itself, an old post town on the Nakasendo, is twenty-odd kilometres south and makes the obvious other half of the day.