National Parks Guide: Arizona's Grand Canyon

— -- As visitors first approach the edge of the Grand Canyon, the wow factor inspired by its grandeur is often accompanied by an instinctive sense that the great void is pulling them into its labyrinthine depths.

It's all part of the allure of the Arizona marvel, one of the world's Seven Natural Wonders and a destination to top any must-see list of national parks in America.

The dimensions are stunning: 277 miles long, 1 mile deep and up to 18 miles wide. Because of twists and side canyons, a full-circuit hike along the rim would cover more than 2,600 miles.

Scott Thybony, a freelance author who has guided raft trips and treks through the canyon for four decades, says the spectacle looms unique and overwhelming even after hundreds of visits. "Every time I go, it's different, it's new," he says. "The inhuman scale of it is hard to get a handle on. You need to hike into it, take a mule down the trail, float the river, fly over it."

Each year, more than 4 million people accept that invitation from all over the world. They come to take pictures of multi-hued cliffs sculpted by water and wind over the eons. But they leave with an indelible life experience that begins with that stomach-flipping sensation on the brink.

"People just drop to their knees and feel like the abyss is sucking them in," says Thybony, who has written several books on the canyon.

For those who linger, especially venturing beneath the overlooks, a whole new sensation unfolds: immersion into a geological time warp that affects each individual differently. Some feel a spiritual envelopment. Some, listening to the breeze swoosh against 2-billion-year-old rock layers, encounter new perspectives on life and mortality.

"What is so great about the canyon is the sense of solitude and space," says Bruce Babbitt, the former Arizona governor who oversaw all of the nation's national parks while serving as Interior secretary. "It has this transforming feeling, and you just step away from daily life."

Babbitt, a geologist, says the canyon remains his favorite park, a place that became so intertwined with his life that he published a literary collection by famed authors and visitors, Grand Canyon: An Anthology.

The place is safe enough so that children, the elderly and those in wheelchairs can enjoy the splendor, yet dangerous enough so that, each year, careless visitors die from falls, heat stroke and dehydration.

For first-time visitors, the big question is how to experience such an overwhelming attraction. You can hike along trails atop the rim, backpack into the abyss for a camping experience, join a multi-day rafting adventure on the Colorado River, ride a mule to rustic cabins or get a bird's-eye view on a helicopter tour.

The mesmerizing scenery cannot be captured in postcards or conjured in poetry. Yet casual tourists find much more to do than gawk. Each day, rangers offer free interpretive classes and treks.

After completing a helicopter tour over the canyon and sidling up to the brink, Richard Parkinson of Richmond, Va., could barely contain his excitement. "It is just fantastic!" he says. "I've had this on my bucket list for years, and there couldn't be anything more magnificent. In all my 69 years, I never knew Grand Canyon was so big."