The Tokamachi tourism association gives the colour season here as mid-October to mid-November, with the peak from late October into the first days of November. Kiyotsu is one of the deep gorges of Niigata, a national place of scenic beauty, and for most of its history people looked at it from a path along the river. That path is closed. Rockfall shut it, and it has not reopened.

What replaced it is a tunnel driven through the mountainside, 750 metres long, with three openings cut in the wall along its length and a chamber at the far end called the Panorama Station. The floor there is a thin sheet of standing water, so the V of the gorge arrives twice, once above and once inverted below. It was rebuilt as an artwork in 2018 by Ma Yansong and MAD Architects and is known as the Tunnel of Light.

The reason the colour works is the rock. The walls are columnar joints, grey and vertical and regular, and the river runs green at the bottom of them. Put maples across that and you get three separate things in one frame, which is unusual. The openings frame it for you, which is either the point or the problem.

During the high season the tunnel uses variable pricing, and on the busiest days entry is by advance booking only, with no tickets sold at the door. Check the official site for the week you intend to go. Buses from JR Echigo-Yuzawa station take twenty-five minutes, and it is a further thirty on foot from the stop to the entrance.