Of all the challenging long-distance thru-hikes in the U.S., few are as difficult as the John Muir Trail. Though hiking trails such as the Pacific Crest Trail or the Appalachian Trail are just as ...

the well-traveled Wonderland Trail around the base of Washington's Mount Rainier is hard to hike but easy to access -- but like the John Muir Trail, you'll have to navigate a permit system.