The Appalachian trail is hiking trail in the Eastern US stretching from the mountains in Georgia all the way to Maine.
Have you ever hiked it?
No, but at least over 2 million people are said to have hiked it. 
I've been on it for about an hour, but that's the extent of my experience with it.
Wow, thats crazy, I didn't know it was longest hiking only trail in the world.