A spectacular tribute to statesman and philanthropist Andrew Mellon.

The discovery site of the "Capitalsaurus," the official dinosaur of Washington, D.C.

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

The fountains of the U.S. Navy Memorial are annually salted with water from the Seven Seas as part of a nautical ritual.

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

This unassuming passageway played a key role in one of the most important events in U.S. history.

An echo chamber with a waterfall wrapped around its base at the Embassy of Canada in Washington, D.C.

Surrounded by traditional homes, this Tolkien-esque dwelling stands out on a quiet street in suburban Maryland.

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

Surrounded by a verdant garden and a backdrop of ivy, a monument to beloved poet Khalil Gibran stands outside of the Lebanese embassy.

A promising candidate for the lost rock laid by George Washington was unearthed, but the hunt is still on.

In the basement of the U.S. Capitol Building is a hidden storage room full of ornate floor tiles leftover from the 1850s.

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

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

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

This statue of the "father of television" stands prominently in the United States Capitol.

The elevator that makes it possible to fly American flags in bulk over the U.S. Capitol

America's Most Wanted's set resides in this tribute to the history of crime and punishment.

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

The sci-fi villain is a little-known inhabitant of the U.S. capital's largest cathedral.

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.

There’s a special club house at the top for the bell ringers.

More than 500 unique and specially designed cases collected by D.C.'s "Harmonica Case Man."

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