Grand Canyon National Park, AZ

Rock of Ages

Want something to talk about back home? Try hiking to the bottom of the Grand Canyon and back. Nothing beats walking 10 miles through 2 billion years of geological history: The rocks, the rapids, the blisters!

Grand Canyon, copyright Grand Canyon Railway

On the other hand, if knees and lungs of steel don't run in the family, confine your activities to the rim. The South Rim, Grand Canyon's most visited section, is laced with "cliffhanging" trails that can be driven, hiked, or biked.

Either way, be prepared for crowds. The southern section of the park is mobbed in summer. You'll be jockeying with the masses for a viewpoint parking spot and competing for a foothold on trails with other hikers -- and mules.