Japan's autumn is usually filed under late November, maples, temple gardens. It starts here instead, in mid-September, high on the eastern flank of the Daisetsuzan massif. Ginsendai is the trailhead for Mount Akadake, about fifty minutes from Sounkyo by way of Lake Daisetsu. What arrives is not a blaze. The conifers hold their green, and into it come the reds of rowan and the yellows of white birch, layer over layer, until the slope reads as one surface.

The road is narrow, and the narrowness decides everything. For roughly ten days at the height of the season, private cars are barred from the prefectural road. You book a seat on the chartered bus from Sounkyo, or you book a slot in the alternating one-way system—uphill and downhill given separate windows of time. Both are reservation only. Arriving on the day is not a plan.

Daisetsuzan is Japan's largest national park. The restriction here dates to 2002, extended from a scheme first applied on the neighbouring Kogen Onsen road in 1997.

Buses run early—the first leaves Sounkyo at six in the morning—and the last one back is mid-afternoon, which makes this a full day rather than a stop on a longer drive. You do not have to climb. Stand near the parking area and the slope is already doing the thing you came for. Some say the colour is better from the trail an hour above; the people who stay below rarely feel short-changed.