Four thousand feet below the canyon rim, the Colorado River continues to slowly eat away at rock formations that created this vast and awe-inspiring canyon.

But this is not the Grand Canyon tourists have come to know and love. This is Grand Canyon West, 90 miles downstream from Grand Canyon National Park, on land owned by the Hualapai Indian Tribe.

Now, the Hualapai are about to do something no one has ever dreamed of before.

Later this month they will open Skywalk — a $40 million glass and steel platform that allows visitors to walk out 70 feet from the canyon's edge and look straight down into the canyon and river below.

"It's an engineering marvel of the world," said Robert Bravo, a Hualapai Indian who is the operations manager of Grand Canyon West....

Not everyone approves of this audacious feat of engineering. Environmentalists and some tribal elders condemn it as a desecration of a sacred American landscape.

"The Grand Canyon deserves much better," said Robert Arnberger, former superintendent of Grand Canyon National Park. "Skywalk is nothing more than a thrill ride, or thrill walk, hanging over the edge."