The "Seinfeld" diner.

One of only two commuter aerial tramways in the United States.

Ride the subways of yesteryear.

This little museum is built on a theater that was once a wildly elaborate speakeasy.

A dilapidated dock tells the story of Titanic's missed arrival.

A hip bar decorated with walls of golden skulls.

Under a glass sidewalk lie the remains of some of Manhattan's oldest buildings.

A Pythagorean funhouse that tries, successfully, to prove that math is the coolest thing ever.

Hidden in Central Park's Ramble is a troublesome cave buried just beneath the surface.

A hands-on traveling collection of the innovative devices of yesteryear.

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

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

This lower Manhattan bar is set up in an old bank vault that rests beneath a skyscraper that hides even more historic splendor.

Elevated freight railway turned wildly successful urban park.

Try not to get slimed in Tribeca.

The world’s oldest and biggest bookstore stocking only mystery, crime fiction, espionage, and thrillers.

This abandoned subway station beneath the Waldorf-Astoria hotel is allegedly used to secretly transport presidents.

Dodge prohibitionists and slide through the telephone booth in Crif Dogs.

This beautiful building in the heart of Manhattan's Financial District was empty for decades.

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

A crumbling hospital from the 1850s on Roosevelt Island.

A terrific purveyor of natural history objects and curios.

A tiny museum housed in a New York freight elevator specializes in the "overlooked, dismissed, or ignored."

A beautiful and abandoned New York subway station from 1904, complete with chandelier.