There are more counterintuitive rivers we could have put on this list, but there are very few with more geologic and hydrologic superlatives. In the 225 miles from Lees Ferry to Diamond Creek, you’ll charge through 42 major rapids and pass Paleozoic walls that are a half-billion years old.
If you’re going to commit to this once-in-a-lifetime trip (and don’t have the skills to paddle your own kayak), float it the way one-armed explorer John Wesley Powell did—in a wooden dory. For 14 to 18 days you’ll float past geologic history, hike to Indian ruins like the famous Nankoweap granaries, and camp on soft sand. Watch OARS’ newly released Whitewater Orientation video—some of which was filmed on location on the Grand—before you go. From $4,898; trips offered May through October.