The Saitama prefectural tourism site gives the colour here as late October to early November. Nakatsu-kyo is a ten-kilometre gorge in the far west of Chichibu, cut by the Nakatsu river between the old Shiozawa district and the settlement of Nakatsugawa, and designated a place of scenic beauty by the prefecture.

The walls are the point. Cliffs rise as much as a hundred metres, broken into odd shapes, and the trees grow in whatever ledges they can hold. From the road the effect is not a broad view but a series of glimpses: red and yellow appearing between rock faces, closing again, appearing further on. It is a gorge to be driven slowly rather than photographed from one spot.

Getting there takes a while, which keeps the crowds down. A Seibu bus bound for Nakatsugawa leaves Mitsumineguchi station on the Chichibu Railway and takes fifty minutes; get off at Aiharabashi and the valley starts at the stop. By car it is a long run west from the expressway, and the road through the gorge is narrow enough that passing an oncoming vehicle needs care.

Azalea in spring, deep green in summer, and quiet for most of the year. But the ten days at the end of October are when the rock and the leaves are in the same frame, and that is what people come for.