For centuries, the only way into this valley was via dangerous mule tracks over passes, snowbound until late in the season. This isolation has left the valley unspoilt, making it ideal for hiking, skiing and white-water sports. It is well worth exploring the grandiose scenery and daring manmade structures, such as the Pont du Châtelet, 100m/328ft above the gorges and Fort Tournoux, clinging to the sheer walls.