This palatial spiral staircase was so unusual the name "snail" was given to the noble family who built it.

Go inside to really appreciate this 500-year-old technological masterpiece.

This historic fort spans more the 300 years.

Two monstrous warehouses. One now holds priceless works of art, the other stands abandoned and dilapidated.

Snack on a partially gestated duck egg.

The East Village tenement from the cover of Led Zeppelin’s 1975 album has a tea shop on the ground floor.

A replica of a 7th-century church hides in plain sight in the middle of the concrete jungle.

This curved Manhattan building was built to house the opulence of John D. Rockefeller's oil empire.

The most unloved grain elevator in Brooklyn was a “Magnificent Mistake.”

A massive forgotten storehouse from 1913 on the Brooklyn Waterfront has a spectacular view of Brooklyn.

In its day this historic fort held 100 cannons pointed in almost every direction to protect New York.

This historic address is home to the beloved ball and is an almost totally empty building among the most expensive real estate in the world.

The remnants of two World's Fairs are here, complete with a 12-story globe, a mini-Manhattan, and a UFO-shaped pavilion.

This mosaic dedicated to John Lennon was tended for years by a Beatles super-fan.

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

Once the tallest building in the world and the site of "the highest dinner ever held in New York" this building now holds the most expensive penthouse in the city.

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

Wall Street has a new heroine, a bronze statue of a small but fierce girl.

A three-story copper skybridge connects two Manhattan buildings with Art Deco luxury.

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

Elevated freight railway turned wildly successful urban park.

A crumbling hospital from the 1850s on Roosevelt Island.

A state-of-the-art medical facility from the Imperial era is now a derelict ruin.

Designed to resemble foreign architecture, this mosque-looking structure was used to pump water to a royal fountain.