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

Seven early Christians were sealed into a cave where legend has it they slept unharmed for centuries.

This modern arts center is built around a gem of late-Baroque architecture.

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

You could be standing at the site of one of D.C.'s most fatal tragedies and not even know it.

There's a 12-foot-tall replica of the Washington Monument hidden under a manhole nearby.

This 16-foot, intricately detailed model of the Gearing-class destroyer has been called the most detailed model ship ever built.

One tiny triangular park commemorates the victims of a yellow fever epidemic—many of whom are buried right below the grass.

This seemingly out-of-place gas station by the Watergate hotel was once described as the most expensive gas station in the world.

One critic described it as "middle Mussolini, early Ramses, and late Neiman-Marcus." Another called it an architectural "natural disaster."

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

An extensive collection of reliquaries containing the bones of saints housed in the largest Catholic church in Venice.

During the Industrial Revolution this “Temple of Invention” was full of intricate miniature machines and gadgets.

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

This fort down the Potomac from Washington, D.C. was once the only defensive fort protecting the capital.

The bank that helped fund the Mexican-American War and the purchase of Alaska met its downfall after helping Augusto Pinochet launder money.

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

Remains of a historic fountain that was mysteriously lost in the demolition of a D.C. traffic circle.

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

Roman-era ships unearthed...

2300-year-old Roman road connecting the empire.

Hundreds of lucky felines haunt the ruins where Caesar was murdered.

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

Largest Roman Catholic church in North America.