Aboveground, Manhattan's Riverside Park provides open space for the densely populated Upper West Side. Beneath its surface run railroad tunnels, disused for decades, where over the years unhoused people have taken shelter. The sociologist Terry Williams ventured into the tunnel residents' world, seeking to understand life on the margins and out of sight. He visited the tunnels between West Seventy-Second and West Ninety-Sixth Streets hundreds of times from 1991 to 1996, when authorities cleared them out to make way for Amtrak passenger service, and again between 2000 and 2020.

Life Underground explores this society below the surface and the varieties of experience among unhoused people. Bringing together anecdotal material, field observations, photographs, transcribed conversations with residents, and excerpts from personal journals, Williams provides a vivid ethnographic portrait of individual people, day-to-day activities, and the social world of the underground and their engagement with the world above, which they call "topside." He shows how marginalized people strive to make a place for themselves amid neglect and isolation as they struggle for dignity. Featuring Williams's distinctive ethnographic eye and deep empathy for those on the margins, Life Underground shines a unique light on a vanished subterranean community.