At twenty-three, Andrew Forsthoefel headed out the back door of his home in Chadds Ford, Pennsylvania, with a backpack, an audio recorder, his copies of Whitman and Rilke, and a sign that read "Walking to Listen." In the year that followed, he faced an Appalachian winter and a Mojave summer. He met beasts inside: fear, loneliness, doubt. But he also encountered incredible kindness from strangers. Thousands shared their stories with him, sometimes...