The west ramp of the Sustenpass starts in the Haslital near Innertkirchen and climbs through the Gadmertal, a deep, quiet, wooded valley that most day-trippers never see. Fuel is down in the valley at Innertkirchen or Meiringen, and the nearest big town is Altdorf, well over twenty kilometres away, so fill up before you go.
The Susten is one of the finest-engineered mountain roads in Switzerland. Built in the late 1930s and early 1940s, partly as a defence project during the war and partly to link the Bernese Oberland with Uri, it climbs steadily on a constant gradient, with wide, flowing bends that are easy to read and a surface that is generally in very good shape. Rock walls rise on one side, and on the other the valley drops away in a drift of glacier-polished slabs and thin waterfalls. Tunnels and galleries protect the road from avalanches, and they can be dark and damp, so lift your visor and let your eyes adjust.
On the way up you pass the Stein glacier, a tongue of ice that once reached almost to the road and has been retreating for decades. A lake of milky meltwater has formed below the ice, and there is a hotel and a car park at the foot of the walk. Sustenhorn and Gwächtenhorn raise their white heads above the pass, and in early summer the snow banks beside the road can stand taller than a rider. The pass closes in winter, usually from late autumn until late spring, so check the opening notices before planning a trip.
Combine it with its neighbours, Grimsel and Furka, and you have the classic Swiss triple, a tour of high passes that one day can barely hold. The best time is early in the morning, when the air is cold and clean and the tourist coaches have not yet begun. At the summit, the thin air makes tea taste better than it has any right to. Watch for cattle on the road, and for cyclists on the long climb.