A commemorative plaque hides a door that leads down to the New York Public Library's underground book bunker.

The highest point on the island known for buildings that touch the sky.

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

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

This elaborate tunnel is the first structure composed of cast concrete in the United States.

This concrete tangle of square pipes has stood as a proud thorn in the city's side since the '70s.

The second building of its name to occupy this location might be the finest flatiron building in San Francisco.

This pharmacist and his patient greet visitors to the National Community Pharmacists Association.

This colonial tavern played host to George Washington, Thomas Jefferson, and other famous early Americans.

This stately building in Alexandria, Virginia was built by Freemasons to honor one of their most famous members.

Daredevil repair workers can worm their way out the access hatch, loop ropes over the apex and rappel down the monument.

The medieval center of the Islamic world was also once the seat of Saladin's sultanate.

A unique post-modern public space in the middle of the Warehouse District in New Orleans.

These locks on North America’s oldest canal are named after a porcine rock formation.

A contemporary fresco movement illustrates the region's rich history.

Memorial built in 1922 in remembrance of WWI casualties.

These unassuming lighthouses have seen the first reading of the Pledge of Allegiance, the first wireless transmission, and more than one mystery.

Infamous marsh filled with toxic waste, World War II-era London rubble, and dead mobsters galore.

Along the Palisades skyline are the ruins of a large mansion built in 1911 and demolished in the 1930s.

Said to be haunted, this tower was constructed by a sugar importer as a gift to his wife.

This unassuming bridge is most likely one of Michelangelo's unfinished masterworks.

A vibrant, 100-foot-tall mural dedicated to Evelyn Nesbit, the tragic icon of the Gilded Age.

There are owls with glowing eyes in Herald Square.

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.