The Arkansas River in Colorado is one of the best rivers for whitewater rafting in the U.S., and the most challenging stretch is the Royal Gorge, running through a narrow canyon with 1000 foot walls. The Arkansas is also the most popular river, and is crowded from May through September. The folks who aren't actually on the river are usually watching it from the suspension bridge over 1000 feet above.

With its long stretch of class III to V rapids, the Royal Gorge has unbeatable whitewaters. There are plenty of named rapids, like the Sledgehammer, Boateater, and Wall Slammer, giving you an idea of what the unnamed ones are like. Besides rapids, you'll hit narrows, big holes, high waves, and lots of steep drops into pools. The highest, coldest flows are in May, when the snow-melt from the Rockies heads down the Arkansas River from the Continental Divide. If the flow is higher than 3200 cfs, rafting is prohibited through the Royal Gorge, and you'll be rerouted to a safer run.

Dozens of rafting adventure companies are happy to provide rafts and guides if you're flying in and can't bring your own gear. They all provide helmets, wetsuits and life-jackets, but some charge extra for use of their gear, so be sure to read the fine print. Most won't accept anyone who doesn't have at least Class III experience for the Royal Gorge whitewater run, so if you have beginners or kids in your party, plan on an easier route like Bighorn Sheep Canyon.

If you want to raft on your own, be aware that recreational use of the Gorge is regulated by the Arkansas Headwaters Recreation Area, and if you put in at any of the possible sites upstream, you'll have to pay a fee for daily use.

After May, it gets really hot in the area, so wear something cool like this Topanga tank from Columbia, that's fast-drying and has UV protection, and these comfy shorts from Cloudveil. Make your feet happy with Salomon's Techamphibian 2 shoes that convert to sandals. And don't forget the sunscreen.