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.

A small token of gratitude from freezing cold journalists who were given a warm haven while covering JFK's inauguration.

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

The early data processor factory founded in Washington for the 1890 U.S. Census went on to become IBM.

America's first federal monument.

This fort down the Potomac from Washington, D.C. was once the only defensive fort protecting the capital.

The school tested mustard gas for the U.S. Army during World War I.

The most accurate timepiece in the world.

When it comes to handsignals (and colonialism) rock always beats scissors.

The oldest house in Washington, D.C. wasn't originally constructed in the nation's capital.

A public art jibe at one of the United States’ oldest and longest-serving senators.

Behind an abandoned storefront is an example of pioneering 1930s gas station architecture.

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

A small triangle of DC grass is the final resting place of one of Sonny and Cher's songs.

A bas relief commemorates the "Nuns of the Battlefield" who cared for soldiers on both sides of the conflict.

Was there a small "backpack nuke" hidden in the attic? JFK apparently thought so.

The sculptor was instructed to add “stallion attributes” to the general's bronze mare.

This unacceptably tall building was the real reason for Washington, D.C.'s skyscraper ban.

A secret greenspace hides atop a Capitol parking garage.

A historic neighborhood church is reborn as a psychedelic arts collective.

This isn't your average roadway—it's actually a National Park and a transportation pioneer.

An amazing example of early-20th-century architecture, this church features marble transported from Utah.

The district's only illusionarium supports free writing programs for local students with every purchase.

Go take a picture with the inventor of the daguerreotype photographic process.