Sometimes urban exploration takes some "Chutzpah" — Yiddish for guts, or more to the point, "balls." New York doesn't reveal its secret nooks and crannies easily. But the rewards are there for those who don't take "no" for an answer.

Want to see the closed City Hall subway station once served by the 6 train? When the southbound train pulls into the Brooklyn Bridge stop and the conductor announces "Last stop. No passengers. All passengers must exit the train," just ignore him. Stay put (and hope a transit cop doesn't throw you off). The downtown train passes through the "ghost" station, closed for decades, on a quick loop around to the uptown track and back to the Brooklyn Bridge stop.

That mild bit of railroad ribaldry is nothing compared to what Robert Diamond went through to uncover the "lost" Atlantic Avenue Subway tunnel. Built in 1844, it is the world's oldest Subway Tunnel — even predating the London Underground. It only operated for a decade before the railroad went bust. The tunnel was shuttered and a city ever focused on moving forward forgot all about the half- mile tunnel.

Even when Diamond located the tunnel on old maps, city officials were none too eager to have him start opening manhole covers and poking around in the bowels of New York. Brooklyn Union Gas went so far as to warn him that if he did find the tunnel he would die of poisonous fumes or be mangled by alligators (seriously!). But Diamond kept on pressing whomever he could find to listen and finally he got permission to open a manhole cover on Atlantic Avenue. And there, just as he guessed from looking at old city maps, was the tunnel!

Every spring the Atlantic Avenue Local Development Corporation again pries open the manhole and invites people down into the tunnel for tours. It's not an outing to be missed! Find out more at www.AtlantiCave.org.

Ever since the old Pennsylvania Station was torn down in 1960, New Yorkers have become a great deal more sensitive — and vigilant — about preserving the city's historic and architecturally notable structures. But now and then, for a variety of reasons, once wonderful building are cut down by the wrecker's ball. And it is right before demolition that urban explorers — those of us passionate about New York's hidden and forgotten spaces — mobilize. Up over the fences we'll climb to get one last look at a bit of New York about to come tumbling down.

I still have a small scar on my right forearm from tangling with the fence that surrounded the old Cunard Line Pier at Little West 12th Street on the Hudson river. Faced with its imminent destruction in the early '90s, a friend and I could not resist visiting one of the last massive piers from the heyday of the great liners.

Even though they were badly weather beaten and damaged, the thick, graceful arches of the pier's iron exterior remained impressive. The interior, however, was a mess, with many of the rooms charred from fires set by the homeless. Broken floorboards and crumbling walls made hallways into nasty obstacle courses. The cavernous main passenger hall, once the scene of near chaos in preparation for every sailing, was now only busy with the comings and goings of pigeons.

The pier has been gone now for a decade, with only the steel of the entranceway arch standing next to the West Side highway. But the pictures we took of the pier hang in my house, alongside those taken in far-off deserts and exotic locales.

For the urban explorer, New York is no less mysterious and intriguing than the Pyramids or the rain forest. And all it takes to go on an adventure is a Metrocard to get you there, and a fair bit of Chutzpah to get you in.