Take a hidden Brooklyn walking tour with the author of ‘The Brooklyn Nobody Knows’

The obsession with exploring New York City started with a game called “Last Stop.” Beginning at age 9, William Helmreich and his father would hop on a random subway line and ride it until the very end, where they would get off to walk around for a while.

“We did this for years,” says Helmreich, now a professor of sociology at City College of New York. “Once we ran out of last stops, we went to the second to last stop, and then the third to last stop, and so on.”

Although teaching now takes up most of his days, Helmreich continues to spend his free time doing what he loves most: exploring New York City, block by block, with no clear destination. He’s already turned his travels into “The New York Nobody Knows” — he affectionately calls the city “the world’s largest outdoor museum” — but quickly realized each borough merits its own tome.

First up is “The Brooklyn Nobody Knows,” out Oct. 11. Helmreich walked all of Brooklyn’s 44 neighborhoods — a total of 816 miles — to create his urban walking tour of the most spectacular and overlooked spots in Brooklyn, guided by interviews with strangers he met along the way and his own unrelenting curiosity.

But knowing the places and things that make up the borough is no substitute for actually doing your own walking.

“I saw a man in Bushwick walking four pitbulls, with two boa constrictors wrapped around his neck, just because he felt like it,” Helmreich recalls. “You can’t do that on Park Avenue and 78th street — you’ll get arrested in a second. Besides, you’re more likely to have a shih tzu.”

We asked Helmreich for some of his favorite places to get you started.

A sample of The Bushwick Collective
Troutman Street and St. Nicholas Avenue, Bushwick

Every building at this five-way intersection in Bushwick features large murals created by street artists, all part of the informal outdoor gallery all around the Jefferson Street stop on the L train known as The Bushwick Collective.

Newtown Creek Nature Walk
Paidge Avenue and Provost Street, Greenpoint

This quarter-mile walkwaycreated by the Department of Environmental Protection has a hidden entrance next to the massive Time Warner Cable warehouse. It brings art and nature into the neighborhood while showing off its industrial character.

Broadway Pigeons and Pet Supplies
1622 Broadway, Bushwick

This shop under the elevated J line in Bushwick is filled with hundreds of pigeons of all colors. “These aren’t the standard pigeons you see in Washington Square Park,” says Helmreich. “You gain an appreciation for these birds once you see them.”

(Alleged) mafia burial grounds
Linden Boulevard between Ruby and Emerald streets, New Lots

This grassy plot is located across the street from where notorious mobster John Gotti once operated — and, reportedly, serves as the burial ground for hundreds of the mafia’s victims.