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

One of the most influential presidents in U.S. history wanted only this plain, elegant monument as his lasting memorial.

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

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

While most wind tunnels test scale models, the "Cave of Winds" was large enough for actual airplanes.

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

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

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.”

"Congress may voluntarily remain in session throughout the summer, in order that our Congressmen may be protected from the intolerable discomforts and dangers of the ordinary outdoor weather!”

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

It was once the base for a series of domestic terror attacks.

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

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

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

An atomic bomb-proof strongbox protects the U.S. Constitution from terrorists and thieves.

Four bald cypress trees in Lafayette Square, across from the White House, mark the southern edge of a 100,000 year old cypress swamp.

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

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

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

This imposing Masonic temple a mile from the White House was the first public library in Washington, D.C.

A cavernous three-story, 43,800-square-foot basement that was forgotten about for 60 years.

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

A monument in Washington D.C. marks the spot from which all other roads were supposed to stem.