Built hundreds of years ago this downtown iron barrier once protected a much despised king.

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

A toxic ghost town sitting atop a massive coal fire.

This dramatic rail curve was once the target of a failed Nazi attack.

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

A decommissioned military complex that's now a modern industrial park.

Fortified medieval tower house with lovely roof garden.

Over 50 exquisite hand-painted Renaissance maps decorate a Medici storage room.

Secret refuge and museum of the Duke of Florence.

No telescopes, no power, no gift shop: The Observatory of Chichen Itza, one of the world's oldest observatories, takes astronomy back to basics.

A historic observatory precariously perched at the "Top of Europe."

This memorial commemorating fallen Swiss Guards of the French Revolution has been called the saddest stone in the world.

This ancient Roman bridge and aqueduct still stands as a wonder of classical construction.

This unmarked and unloved Manhattan subway grate created one of the most iconic images in American cinema.

“Invented in Key West, Perfected in Brooklyn."

The most confusing clock in New York.

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

The famous boat that once ferried Bogart and Hepburn still floats in Key Largo after being abandoned for years.

Discovered by cows, these upstate New York show caves are presented with a healthy dose of psychedelic folk art.

The lost town of Neversink, sunk by New York City.

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

An accidentally hidden library containing the ephemeral history of New York.

New York City's smallest piece of private property.

This lovely, if imposing, piece of Canadian gothic is possibly the most photographed hotel in the world.