The Rio Grande travels 1,900 miles from Colorado's Rocky Mountains to the Gulf of Mexico, threading through classic quilted farmland, barren deserts, and coastal forests. Its most beautiful stretch lies in an unexpected place, the remote southwestern corner of Texas. Here, on the western edge of Big Bend National Park, Santa Elena Canyon's limestone walls rise some 1,500 feet into the sky, rivaling the Grand Canyon in size and exceeding it in beauty. The best place to appreciate the view is from the river and the best way to make it to this remote stretch of water is on a two- or three-day rafting trip through cataracts like Rockslide, a Class IV tumble. After all that whitewater, the most memorable moments are defined by stillness. At the bottom of the canyon, it is so silent you can hear a drop of water shear off the oars. Lay back in the boat, look up, and ponder the forces that built this cathedral of rock.

More information: The Big Bend area is packed with other attractions. Check out Marfa and Terlingua.