One of the last Jazz Age "Wonder Theaters" in New York City.

This sculpture by artist Fritz Keonig survived the 9/11 attacks and now stands as a monument to the victims.

The "Seinfeld" diner.

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.

This whimsical group of statues is a favorite of children who love to climb all over Lewis Carroll's beloved characters.

The name of this famed hospital was once a byword for the horrors of medical and psychiatric care.

Mysterious 500-year-old tapestries depict a unicorn hunt.

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

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

Whisper secrets in a busy station only to be heard on the other side of this acoustic arch.

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

Elevated freight railway turned wildly successful urban park.

Amid the bustle and noise of the Financial District hides a secluded garden oasis above the city streets.

A terrific purveyor of natural history objects and curios.

A discreet little stairway on St. Nicholas Avenue leads to a quaint and unexpected cobblestone street of 19th century wooden rowhouses.

The oldest house in Manhattan is now a museum that remembers the home's sordid history of scandals, vice-presidents, and ghosts.

Berthed at the Charlestown Navy Yard in Boston, "Old Ironsides" is the oldest commissioned warship still afloat.

The 5.5-mile ring of steel posts around the Capitol Building is one of the largest (and most uniform) of its kind in the world.

The preamble to the U.S. Constitution written entirely from vanity license plates hangs in the Smithsonian museum.

A derelict bit of infrastructure from the canal that once ran through D.C. is landlocked in the heart of the city.

While most wind tunnels test scale models, the "Cave of Winds" was large enough for actual airplanes.

Washington's iconic carousel has a nice piece of Civil Rights history.

A heroic pigeon that, through a barrage of gunfire, delivered a message that saved over 100 lives in World War I.

Perhaps the most scandalous statue of America's first president.