Some of Andorra's Pyrenean ski resorts offer another, more unusual, attraction. While the skiers hurtle down the slopes, past snow-laden pine trees and frozen lakes, many of them will have no idea that divers are exploring the strange underwater world of those mountain lakes. The visual rewards for anyone prepared to venture into the chilly depths are soaked in the other-worldly clarity of the light that streams through the filter provided by the white-blue ice above.