Rising to the west of Sunwapta Pass, the dividing line between Banff and Jasper Parks, the massive Columbia Icefield is what the Icefields Parkway is all about: the largest icefield and most accessible glacier in the Canadian Rockies, seemingly endless square miles of solid ice sitting high atop the Continental Divide. Visibly shrinking throughout the 20th century, the icefield is still immense, and you can get an up-close look by joining the very popular “Ice Explorer” tours ($C30; 877/423-7433) operated by the Brewster company, which leave every 15 minutes and travel out onto Athabasca Glacier.

  Overlooking the icefield from across the Icefields Parkway is the modern Columbia Icefield Centre (daily May–Oct.; free), a mini-museum of glacial lore operated by Parks Canada. If you want to experience the icefield up close, buy a ticket and take one of the Ice Explorer tours; don’t simply walk across the highway and clamber up, since it only takes one false step to fall to your death into one of the very deep but invisible crevasses that crisscross the glacier.