In January, a glass-bottomed, horseshoe-shaped walkway over the Grand Canyon--protruding 70 harrowing feet--will be unveiled. The Skywalk was envisioned nine years ago by David Jin, a tour operator specializing in trips to the Canyon's westernmost side, home to the Hualapai tribe. The tribe liked the idea, and Jin tapped Mark Johnson, a Las Vegas-based architect, for the design. The Skywalk has six-foot-tall glass walls, and is built to bear more than 71 million pounds, withstand winds over 100 miles per hour, and endure an 8.0-magnitude earthquake within a 50-mile radius. Still, says Johnson, "it's going to take some courage to step out there. Looking through a glass floor is intense." Views of the Colorado River, 4,000 feet below, come with a steep price. You must first book a tour of the tribe's grounds (877/716-9378, destinationgrandcanyon.com). The cheapest ($29) includes a walk through dwellings and an outdoor craft market. Only then can you test your mettle on the Skywalk, for an extra $25.