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.

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

Senators used to relax in the nearly forgotten marble tubs now hidden in the U.S. Capitol Building's basement.

"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!”

Before Nixon, "watergate" meant canals.

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.

An easily overlooked memorial to a Ukrainian famine-genocide that killed over 4 million people.

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

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

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

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

This sandwich shop has a century-old elevator behind a sheet of plexiglass.

Rumor has it the uncarved lump behind the three famous suffragists is reserved for the first woman president.

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

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

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

The most decorated dog of World War I is preserved in the Smithsonian.

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

Home to items never before seen by the public.