A visitor to these stark and imposing lands of the Hualapai Indians on the western rim of the Grand Canyon knows what sensation is being promised at the journey's climax. After driving for a half-hour over bone-jolting dirt roads some 120 miles from Las Vegas, you take a shuttle bus from the parking lot, not far from where helicopters are landing, and construction is proceeding. You deposit all cameras at a security desk, slip on yellow surgical booties and stride out onto a horseshoe-shaped walkway with transparent sides and walls that extends 70 feet into space, seemingly unsupported. Welcome to Grand Canyon Skywalk.

Below the floorÕs five layers of glass (protected from scratches by the booties) can be seen the cracked, sharp-edged rock face of the canyonÕs rim and a drop of thousands of feet to the chasm below. The promise is the dizzying thrill of vertigo.

The Skywalk, which opened in March and cost more than $30 million, will end up paying for itself if it keeps fulfilling that promise of amusement park vertigo, particularly because each visitor taking the brief walk over the abyss must pay at least $74.95 for a tour package. But a similar thrill can be had with greater intensity just a hundred yards away on ordinary ground, where tourists tentatively edge toward a precipice without guardrail or fence, and look across the ravine at a great rock formation that bears some resemblance to a giant eagle, its wings outspread. In that spot the sense of grandeur is far more palpable than on the pedestrian walkway, which within a few moments can seem as routine as a glass-bottom boat in the Caribbean.