The Comal River is famously Texas's shortest navigable river. It is also famously the site of the first Schlitterbahn water park. Gently running beneath overhanging foilage, this is a river well-suited to floating.

Take a rafting trip down from Canyon Dam for an excellent intermediate run. This river has a bracing swiftness, but not so swift that you can't watch the scenery and watch for wildlife among the trees and bushes.

Boquillas Canyon marks a long and leisurely run between canyon walls that climb to 1,200 feet, but despite their size, are more awesome than oppressive.

You can't even reach this canyon without four-wheel drive, it's so remote. It's also pretty short; the run's only ten miles long, but it's ten miles run between limestone cliffs that are almost as tall as Santa Elena's walls (these climb up to 1,400 feet).

Santa Elena Canyon is the most popular part of the Rio Grande to raft, not just because it's about as accessible as accessible can get, but because it's gorgeous.

The Lower Canyons are daunting. A typical route down this portion of the Rio Grande takes anywhere from five to ten days and the rapids range from Class II to Class IV in intensity.

The Rio Grande is more than a river, it is a boundary between countries. But even so, it remains remote and lonely, the Chihuahuan Desert surrounding it closely as opposed to city after city.