Accessible only by boat, this centuries-old island fort never saw troops or combat.

A small Second Empire-style building is one of only seven remaining lighthouses on the Hudson River.

The life of one of FDR's possible mistresses is preserved in her palatial Hudson Valley mansion.

100 massive sculptures in the Hudson River Valley.

The final resting place of the Seminole Indian chief who fought against government occupation in Florida.

A stunning, two-tiered waterfall made famous by poets, artists and the legend of a ghost dog.

An eerie, decaying ghost town destined to fade into the forest.

The home of possibly the least-loved U.S. president stands as a sort of unpopular Monticello.

The oldest farmer's market in America is so ancient it was approved by the King of England.

The internal railway of one of the biggest steel plants in America has been transformed into a linear park with unique industrial views.

A field of nothing but boulders which resembles a giant's gravel driveway.

A former plant in one of the hubs of U.S. steelmaking has been turned into this museum celebrating the history of American industry.

Enormous piles of historically significant stones, dumped by Congress in a forest, and abandoned for 60 years.

A clone-tree in Washington Square Park sprung from seeds that went to the Moon and back.

Buildings from the fictional planet of Tatooine still litter the Tunisian desert.

These recently uncovered walls are all that's left of Washington, D.C's first defense contractor.

A tiny monument to the unsuccessful attempt by Thomas Jefferson to place the prime meridian in Washington.

This mysterious structure by the Washington Monument is a flood barrier designed to protect the White House against rising waters.

A portal into the bricked up canal that runs through the heart of Washington D.C.

A diminutive plaque recalls the treetop sniper who almost killed Abe Lincoln.

The discovery site of the "Capitalsaurus," the official dinosaur of Washington, D.C.

A Civil War fort in the middle of Washington, D.C. has been swallowed by a forest.

The national park was once a plantation estate.

There’s a hidden military meme engraved on the World War II Memorial.