Silver, cars, a piano, bodies, a train, ships, a giraffe, t.p., and more: Uncovering the secrets beneath New York Harbor

The steady transformation of New York's waterfront from wasteland to playground means more of us are spending time along the city's edge. That can lead a person to wonder: What, exactly, is down there? Until recently, we had patchy knowledge of what lies beneath the surface of one of the world's busiest harbors. What we did know came largely from random anecdotes, and depth soundings done the way Henry Hudson did them—by rope and lead sinker.

This first GPS-era picture comes from the team at Columbia University's Lamont-Doherty Earth Observatory, who have methodically swept the lower Hudson with state-of-the-art sonar. LDEO's Dr. Frank Nitsche stitched together their data, along with several other researchers' work, into this elegant color-keyed map, which we've supplemented by talking with sea captains, historians, and the divers pictured above. There's a whole other city down there. Here and on the following pages is your guide.