Southern Alps — Ōi Headwaters

The valley that comes after Kurobe. Same idea — follow the river — except that here you are going uphill.

The place

The headwaters of the Ōi river in Shizuoka prefecture, in the heart of the Akaishi range (the Southern Alps). From the Hatanagi reservoir the valley narrows as it climbs.

Measured elevations run from 669 m to 2,142 m. The walls are not as sheer as Kurobe’s, but what defines this ground is that ridge stacks behind ridge until depth becomes hard to read.

The terrain we built

8.0 km square. Conifer and broadleaf forest mix across the slopes, changing colour with altitude.

Haze pools in the valley morning and evening. Backlit ridgelines wash out and distance stops registering, so you get the specific problem of seeing something clearly and having no idea how far away it is.

What it is like to fly

You enter over the reservoir surface and follow the river up. The difference from Kurobe is that the ground comes up to meet you. Hold what feels like a steady altitude and your height above the ground quietly decreases.

And it is always upstream that the outs run out. The entrance is wide; the deeper you go, the narrower it gets. The decision to turn back is one you make before it is tight, not after.

• Stalls and turns — why you never slow down in a gorge