An uber-secure, windowless tower of doom in the center of Manhattan is an NSA spyscraper.

Nondescript elevator doors open to reveal a stunning, surreal world.

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

A very classy 1920s-era bar right in Grand Central Station.

The world's oldest hologram gallery and the labyrinthine laser laboratory of a holography pioneer.

The "Seinfeld" diner.

A pedestrian island in the middle of world-famous Times Square emits a strange (and purposeful) humming noise.

A room in New York City that contains 250 cubic yards of dirt worth a million dollars.

More gold than anywhere else, ever.

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

New York City's smallest piece of private property.

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

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

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.

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

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

A terrific purveyor of natural history objects and curios.

In the woods of New Jersey lie the ruins of a munitions village abandoned after World War I and the remnants of a 1920s wooden racetrack.

One of New York's best collections of pinball is hidden in a secret bar in the back of this laundromat.

Built to test magnetically levitated elevators, the tower also boasts Germany's highest visitor platform.

One of two lighted lanterns hung in the church belfry on the eve of the Revolutionary War to warn that the British were on their way.

Twice a year, visitors can tour the desolate site that birthed the Atomic Age.

"Not too many people can say they've had a nuclear bomb dropped on them, not too many would want to." — Walter Gregg.