Architecture lovers won’t stop touching the National Gallery's 19.5 degree marble prow.

The most accurate timepiece in the world.

The national park was once a plantation estate.

A three-story tower of books about Abraham Lincoln is one of the more unusual monuments to the president.

A haunting tribute to pioneering photographer Clover Adams.

This lonely waterfront memorial to the men of the Titanic was erected by the "Women of America."

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

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

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

The site of the climactic scene from the classic horror film is now a historic landmark.

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.

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

An overlooked memorial honoring the local Washington residents who died in World War I.

The beloved statue at the National Academy of Sciences is oh so inviting to sit on.

Largest Roman Catholic church in North America.

Bar full of oddities, specimens, artifacts and homages to the great dime museums of the past.

This stunning blue and gold room changed cities twice before becoming part of the Smithsonian.

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

A museum cafe showcases Native American dishes and indigenous ingredients from across the Western Hemisphere.

A hidden passageway now marks the site of an assassination attempt on Ronald Reagan that some say broke a 140-year-old curse.

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

With over 100 jam-packed rooms to explore plus elaborate tea services and events, the Mansion on O Street is a hidden treasure.

A hidden gem on the lawn of the U.S. Capitol Building designed by landscape architect Frederick Law Olmsted.