Concrete Progress is an ongoing series of columns by Peter Brewitt devoted to exploring America’s infrastructure. It is part of Orion’s Reimagining Infrastructure project. Photograph by Nicolas Vollmer.

In the beginning, New York City was a wilderness. The Hudson River flowed in from the forested Adirondacks to the little archipelago where Long Island meets the east coast, the spruce-cloaked hills rose on Manhattan Island, and beaver worked their way through the swampy bottoms. According to landscape ecologist Eric Sanderson (from an excellent article in National Geographic a few years ago), this confluence of ecosystems was incredibly bio-diverse. It was the kind of place that, had history unfolded differently, might be a national park today.

But of course, history didn’t go that way—the Dutch bought Manhattan, the city boomed, the immigrant ships poured in, and, eventually, despite the landscape’s natural productivity, New York outgrew its food supply and had to ship in its sustenance by train. The trains were hazardous to pedestrians, though, and in the early 1930s, the city decided to build an elevated track, thirty feet above the streets of Chelsea, in Manhattan. It was called the High Line.

By 1980, American transport had shifted away from trains, and no one used the High Line anymore. The city itself was on what seemed to be a downward spiral. But as everyone knows, New York shook itself off in the 1990s and became the safe, vibrant metropolis that exists today.

The High Line, though, was left out. Creaky and overrun by weeds, it became a prime target for demolition, until two guys in the neighborhood, Joshua David and Robert Hammond, founded Friends of the High Line in 1999. They set about trying to use this unique airborne pathway as public space, and over the next few years, the Friends partnered with architects, nonprofits, and the City itself to reimagine the High Line. The vision eventually coalesced in the form of an elevated park, where nature could return to the city, and the people of the city could return to nature. Visually creative and structurally sound, the restoration project began in 2006. (It’s also economically productive: the tax revenues the space created outweighed the price of the project; 90 percent of the annual operating costs are met through private funding; and the surrounding apartments have become more valuable due to their views of and access to the High Line.)

Now, cedars, serviceberries, maidenhair ferns, and 207 other kinds of plants grow along the old tracks, 161 of them native species. And in 2011, five years after the work began, 3.7 million people walked the High Line. That’s about the same number of visitors to Yosemite National Park.

I had to see the place for myself, so on a humid day this summer I took off from the Association for Environmental Studies and Sciences conference and walked a couple miles north to Chelsea. The concrete landscape greened up a little in TriBeCa, and some blocks later a flight of stairs rose up from Gansevoort Street. If it hadn’t been for the High Line sign, this would have felt like any other urban stairway—street noise and steel girders—until I emerged in a birch grove. Ahead of me, shaded by high-rise apartment buildings, stretched a path through the woods.

I had imagined the High Line as a sort of secret garden, a little seam of unruly nature that you enter through a portal and wander in for days. In truth, it was more imaginative than that. Instead of a 1.45-mile strand of pretend-wilderness, the park is at once very much about nature and very much about the city. As I walked through puffy purple shrubs and orange flowers (everything was blooming), I found the industrial past of the High Line, not hidden, but woven into the restoration—the cracks in the walkway cleverly spread into ridges that allowed the vegetation through before disappearing into the undergrowth. The old train tracks run among the trees and through sculptures molded out of railroad components. You can get an ice cream and a cold drink around the halfway point.

Above and beside and below the path is the city—there is a great view to the east down 23rd Street, and another to the west across the water to New Jersey. At times the woods are fairly thick, but even so, I was always aware that I was in New York City. It’s just that I’d never imagined New York City like this—a strand of little wetlands and blooming wildflowers and songbirds flitting through the dogwoods. I hiked down to the end of the line at 34th street, looked north to where they are already planting the next extension of the park, and dropped back down to street level.

Peter Brewitt has wondered about infrastructure ever since a flood kept him away from three days of kindergarten. He wrote his doctoral dissertation on dam removal politics at the University of California, Santa Cruz, and will begin an Environmental Studies professorship at Wofford College this fall. In his academic work, he researches the ways people decide to restore and remake their environments.