Nearly five million people travel here each year; 90 percent first see the canyon from the South Rim with its dramatic views into the deep inner gorge of the Colorado River. So many feet have stepped cautiously to the edge of major overlooks that in places the rock has been polished smooth. But most of the park's 1,904 square miles are maintained as wilderness. You can avoid crowds by hiking the park's many trails or driving to the cool evergreen forests of the North Rim where people are fewer and viewing is more leisurely. The Grand Canyon boasts some of the nation's cleanest air, with visibility on clear days averaging 90 to 110 miles.