Bring your own cardboard to the slippery slopes of concrete hidden in a neighborhood park.

An artsy hidden staircase leads to breathtaking views of San Francisco.

Detailed facade of a brownstone in Boerum Hill.

Tucked in the back of this amazing antique store is an important piece of medical history.

Reverend Jen's unique museum/living room showcases her troll collection.

A living archive of urban activism and space reclaimed.

The feral felines of Roosevelt Island have a small army of allies and an abandoned hospital all to themselves.

This cemetery has graves dating back to the 17th century, including the city's oldest carved tombstone and an ominous cryptogram.

This former crime corner has been turned into an eclectic community center.

An unassuming secret door once led to a legendary watering hole.

New York City's smallest piece of private property.

Manhattan and the Bronx have been playing tug-of-war over this former island neighborhood for more than a century.

This small New York museum celebrates the mountainous artwork of a Russian mystic.

A quiet and contemplative oasis in the middle of New York's bustle and riot.

A staggering collection of photographs depicting medical, social, and historical change.

A band of aerialists and circus performers putting on incredible shows in East Williamsburg.

Volunteer-run library dedicated to exploring five decades of activism history.

A tree that grows parallel to the ground was declared Brooklyn's "crowning curio" by the poet who saved it.

Harlem park dedicated to compulsive hoarders killed by their own junk.

A New York garbage depot holds a secret collection of weird and wonderful refuse.

Unique antiquarian shop specializing in globes, maps, and prints.

A treasure trove of artifacts, books, and artwork from the "golden age" of exploration.

Cryptic messages embedded in the New York City sidewalk.

Down a stairway in the East Village, you could once read a plaque describing an alternate history of a fictional version of Manhattan.