"In 2009, while thru-hiking the Appalachian Trail, Robert Moor began to wonder about the paths that lie beneath our feet: How do they form? Why do some improve over time while others fade? What makes us follow or strike off on our own? Over the course of the next seven years, Moor traveled the globe, exploring trails of all kinds, from the miniscule to the massive. He learned the tricks of master trail-builders, hunted down long-lost Cherokee trails,...