At 207 feet, one of the world's longest continuous escalators.

America's first federal monument.

This simple stone memorial remembers a secret, Geneva Convention-defying interrogation base from WWII.

The graveyard holding the remains of George Washington's slaves was forgotten for nearly 200 years.

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

Light bulbs, scrap wood, and tinfoil comprise this homemade throne of the gods.

The preamble to the U.S. Constitution written entirely from vanity license plates hangs in the Smithsonian museum.

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

This colonial tavern played host to George Washington, Thomas Jefferson, and other famous early Americans.

The narrowest house in America is seven feet of pure spite.

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

A derelict bit of infrastructure from the canal that once ran through D.C. is landlocked in the heart of the city.

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

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

A muscular Art Deco monument represents the struggle between regulators and unbridled markets.

The 5.5-mile ring of steel posts around the Capitol Building is one of the largest (and most uniform) of its kind in the world.

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

The winding route passes through an enclosed alleyway, two tunnels, and leads to the White House basement.

A heroic pigeon that, through a barrage of gunfire, delivered a message that saved over 100 lives in World War I.

This taxidermy horse was a Civil War hero.

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

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

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

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