“Otherworldly” is how I describe our experience trekking Patagonia’s Perito Moreno Glacier. At 19 miles long and three miles wide, Perito Moreno is the third largest reserve of fresh water in the world…and it is one of only a few glaciers left that is still advancing. Upon approaching this colossus of ice, you see arêtes spiking to 20 stories above Lago Argentina—but the ice actually starts at a depth of 50 stories below the water level. The glacier is surrounded…