Art deco landmark on the outskirts of Washington, D.C.

There’s a special club house at the top for the bell ringers.

A historic ruin just 20 feet away from a busy highway onramp.

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

The only Civil War battle in Washington D.C. took place near this highest natural point in the city.

One of the largest artillery pieces in the world sits in a Washington D.C. parking lot.

Members of Congress have traveled between the buildings on Capitol Hill for a century hidden from tourists, press, and storm clouds.

Those with a sharp eye can find the hidden image of a German Shepherd on the memorial's Mural Wall.

This stately mansion, built in 1787 by America's first Secretary of the Navy, is rumored to be one of the most haunted buildings in Washington, DC.

The span is crooked and made from two older recycled bridges.

The most accurate timepiece in the world.

Decades before the scandal, this staircase on the river was a literal "water gate."

The oldest building in the District of Columbia was preserved because of a mistaken connection to George Washington.

A hoard of sky catalogs, astrophysical journals, even the works of Galileo and Copernicus.

The actual model from the original "Star Trek" series is now on display at the National Air and Space Museum.

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.

Fittingly, America's museum of architecture is itself a magnificently designed old building.

A derelict bit of transportation infrastructure hidden in the woods.

During the Industrial Revolution this “Temple of Invention” was full of intricate miniature machines and gadgets.

A tiny piece of the Moon is embedded in this stained glass masterpiece.

A painfully obvious spy house sits right across the street from the Russian Embassy.

There's a 12-foot-tall replica of the Washington Monument hidden under a manhole nearby.

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