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

Look closely and you’ll notice that the color changes a third of the way up the tower.

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

The grand marble structure next to the White House is Andrew Carnegie's temple to Pan-American diplomacy.

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

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

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

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

The romance of early commercial flight still fills this Art Deco destination.

Bizarre Cavern.

The school tested mustard gas for the U.S. Army during World War I.

The system of air guns are fired off remotely to scare any trespassing avians.

Right next to departures—how convenient!

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

This church built atop a gas station promises to "equip you for the next stage in your life’s journey."

The Pentagon is so large that it was planned like a city, complete with internal highway infrastructure.

Born a slave on the Arlington estate, Parks dug the first graves at Arlington National Cemetery, and was buried there, too.

The naval commander’s proudest moment in battle is memorialized in this unique tomb at Arlington Cemetery.

The controversial urban planner who designed Washington, D.C., was buried in Maryland, and can presently be found in Virginia.

This isn't your average roadway—it's actually a National Park and a transportation pioneer.

Soldiers were buried next to Lee's house in the center of Arlington Cemetery to dissuade the general from reclaiming his property after the war.

This forgotten boat elevator was an engineering marvel in its heyday.

The rogue roots are gradually consuming some of the historic marble grave markers.

This rare triple-jurisdiction drawbridge passes through Virginia, Maryland, and Washington, D.C.