From afar, the Rhone glacier looks pristine, but on closer inspection the surface is covered with white blankets to slow the melting of the rapidly retreating ice.

The dusty, white fleece covers stretch out over a huge area near the glacier's edge, some in rumpled piles alongside sand, rocks, a few wooden planks and a ladder on its side. A red and white Swiss flag provides the only dash of color.

The blankets look like tents in a vast deserted refugee camp, out of place in the Alpine setting. But hiding beneath them is a Swiss tourist attraction: a long and winding ice grotto with glistening blue walls and a leaky ceiling that has been carved into the ice here each year since 1870.