"If I mistake not, it will be a great resort for tourists and madmen who like climbing mountains at the risk of breaking their necks."
--Collingwood Schreiber, Canadian Pacific Railway chief engineer, 1884

When first confronted with the swimming-pool hue of Moraine Lake in Canada's Banff National Park, incredulous tourists have sometimes accused local hoteliers of dyeing the water. Tour operators have broached dubious theories too, about how a crystalline structure of the meltwater causes the otherworldly tint.

To find the real reason--or to escape the other visitors clambering on the rock pile that provides this classic view--you can paddle or hike to the opposite shore. The Wenkchemna Peaks loom larger and the breeze chills as you approach the lake's glacial headwaters, where vast fans of scree and snow above a sandy creekbed offer clues. During the last ice ages, giant rivers of ice sculpted the area. As the glaciers retreated, they shed piles of debris, or moraines, often damming the melting ice. The remaining glaciers continue to creak down the mountains, slowly grinding whatever's in their path. Boulders become rocks; stones shrink to pebbles; granules dwindle to fine particles. And as the glaciers melt into rivers and lakes, the tiniest specks, called rock flour, are suspended in the water. This rock flour is what scatters sunlight and gives Moraine its milky opalescence.

Pry your eyes from the water and you'll discover other marvels, starting with the Lyall's larch, an oddball conifer that crowns the treeline with a blaze of gold before shedding its needles to withstand the winter. Listen for hoary marmots' whistles and watch them bodysurf on patches of alpine snow. Linger for glimpses of tiny, big-eared pikas scurrying to make hay while the sun shines (they don't hibernate, so they harvest and dry plants to survive the long cold season). Or consider the mountains. Formed as an ancient seabed, they were heaved skyward when the Pacific and North American Plates collided 100 million years ago. The staggering power of their creation is evident throughout this stretch of the Rockies, in the crazy angles of the sedimentary bands, crumpled rock folds, and ragged crags. And it's this sense of almost unfathomable scale that beguiles tourists and rock-climbing madmen alike. --Debra Jones