Grand Canyon of the Yellowstone

This isn't one trail so much as a choose-your-own-adventure along the rim of a canyon that makes most gorges look like drainage ditches. The Grand Canyon of the Yellowstone stretches roughly twenty miles, with walls streaked in yellows, oranges, and reds that look like someone took a blowtorch to a painting. Most visitors work the South Rim and North Rim trail networks near Canyon Village, hopping between overlooks connected by paved paths and wooden boardwalks. The showstopper is the view of Lower Falls -- a 308-foot plunge that dwarfs Niagara in height. If you want to earn it, take Uncle Tom's Trail, a steel staircase bolted into the canyon wall that drops you partway down with a gut-punch view of the falls. The rim walks themselves are mellow and partially wheelchair-accessible, but the side trails into the canyon will remind your knees who's boss. This area rewards everyone from stroller-pushing families to photographers willing to wait out the morning mist.