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

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

Legend has it that President Grant’s frequent drinking in the lobby gave rise to the term “lobbyist.”

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

The monument's pointy aluminum tip has been melted down by repeated lightning strikes.

The unique traffic pattern named for an influential urban planner is also known as the Pedestrian Scramble.

A little marble compass above George Washington's (empty) tomb in the Capitol marks where D.C.'s four quadrants intersect.

A much-maligned monument to teetotalism.

An unassuming, powerful monument north of the U.S. Capitol bears witness to the resilience of Japanese Americans during a time of grave injustice.

The national park was once a plantation estate.

Government testing at the asylum briefly explored using marijuana as a "truth serum" on Nazi prisoners of war.

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

The most accurate timepiece in the world.

Once the supplier for noteworthy projects like the National Cathedral, this old brickworks now lies abandoned.

The remains of Martha, the last known passenger pigeon, serve as a tool to educate about conservation.

The "lovely red Vega" of the legendary record-settling pilot.

The house where John Wilkes Booth conspired with his co-conspirators.

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

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

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

The walls of the iconic dome are hollow and have a secret stairway.

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

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

Home to items never before seen by the public.