The second leg of the 5-stage Tour du Val d’Hérens links two side valleys: the Val d’Hérémence and the Val d’Arolla. The first part of the hike is a flattish walk the length of the Lac des Dix. A steep climb leads up to the Col de Riedmatten, which links the two valleys. The final stretch of hike is a steady descent to the village of Arolla. The hike starts at the crest of the Grande Dixence, the world’s tallest gravity dam. From here it leads along the western shore of the Lac des Dix: Switzerland’s largest artificial reservoir, with a capacity of 400 billion litres of water. The setting is spectacular, with a parade of snow-capped peaks, draped with glaciers, forming a sparkling backdrop beyond the lake. The trail climbs above one of the glaciers to a pass made famous by the world’s toughest ski mountaineering race. The Patrouille des Glaciers, held every other spring, sees teams of three race from Zermatt across the mountains and glaciers to Verbier, and has won a reputation as the world’s toughest team competition. The steep and narrow climb to the Col de Riedmatten (2,918 m) is one of the contest’s great challenges – although the ascent in summer should not pose problems for experienced mountain hikers. From here, the trail leads steadily down to Arolla in the neighbouring valley. Before starting the hike, if time permits, it is worth calling in at the visitor centre at the foot of the dam to learn about the region’s geology and wildlife. The centre also reveals some of the secrets of the pioneering Grande Dixence complex, which unites a vast network of reservoirs, underground tunnels, pumping stations and power plants to form Switzerland’s largest hydro plant. Highlights: Grande Dixence – world’s largest gravity dam, visitor centre (free admission) and cable car Lac des Dix – flat trail along Switzerland’s largest reservoir, framed by snowy peaks Col de Riedmatten – dramatic climb to an iconic mountain pass.