The Appalachian Trail is a footpath the extends up the east coast from Springer Mountain in Georgia to Mount Katahdin in Maine. It is approximately 2,100 miles long. For more information about the Appalachian Trail, check out these links:
Here are some links to other organizations that work with hikers and help maintain the trail.
Appalachian Long Distance Hiker's Association
Of course, the best way to experience the trail without walking it, is to read journals. Here is a list of some of my favorites.