High up in the French Alps, Tignes is one of France's best known winter resorts. That's of course thanks to its snow, but also a more unexpected asset: its water. At 2,100 metres above sea level, its frozen lake in winter attracts divers in search of chilly thrills. The lake results from the 1950s construction, lower down in the valley, of a gigantic 180-metre-high dam, the highest in France. This monumental project completely reshaped the region and the destiny of the village.