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

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.

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

The Lincoln Memorial has inspired many, even though a word on the inscription appears to be spelled incorrectly.

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

A gift from Japan, 17th-century lantern stands among the cherry trees at D.C.'s Tidal Basin.

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

Engraved in stone here are the signatures of everyone who signed the Declaration of Independence.

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 tiny monument to the unsuccessful attempt by Thomas Jefferson to place the prime meridian in Washington.

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

After James Madison's death, his wife and former First Lady Dolley Madison lived in this yellow building near the White House.

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

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

D.C. once had its own tiny rival to the New York Stock Exchange.

A line of blue paint marks the route of the inaugural parade.

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

A three-story tower of books about Abraham Lincoln is one of the more unusual monuments to the president.

This Masonic lodge was the first major private building to be constructed in Washington, D.C. after the Civil War.

Over the last century, this elegant columned facade has been home to the headquarters of a bank, several nightclubs, and a restaurant.

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

The unique traffic pattern named for an influential urban planner is also known as the Pedestrian Scramble.

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