It’s one of the seven wonders of the natural world, but it doesn’t need any titles to impress; the numbers speak for themselves. The formidable Grand Canyon is 446 river kilometers (227 miles) long, up to 29 kilometers (18 miles) wide and 1.6 kilometers (1 mile) deep, and its walls offer a striking mosaic of geological colors and erosional forms that could put any museum to shame -- particularly when the colors change at sunrise and sunset. Add to the mix a few curtain-like waterfalls, Native American ruins and curious desert-dwellers, and you’ve got yourself a postcard-perfect vacation.