Moses Gates is a professor of demography at Pratt Institute. As he reveals in Hidden Cities (Tarcher/Penguin), he’s also a man with complicated experiences exploring urban spaces from New York to Paris to Sao Paulo to Odessa. His passion: places people aren’t meant to go. He prefers the physically dangerous and legally dubious—down sewer and subway tunnels, up bridges and cathedrals.

Hidden Cities provides a compelling introduction into this international brotherhood of adventurers, though Gates’ self-satisfaction and unnecessary personal details sometimes clot his tale. It’s a fascinating study of the liberatory power of ignoring pointless prohibitions. But in the end, it’s elegiac. In the post-9/11 world, such clandestine urban explorations have become more difficult and dangerous—because of authority, not physical reality. —Brian Doherty