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

An ear-piercing buzzer calls lawmakers to a vote with a series of long and short rings to form coded messages.

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

Corn-inthian columns with a uniquely American take on neoclassical architecture.

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

A 1,100-ton train fell through the floor in 1953. Workers got it patched up in just 72 hours.

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.

A hidden passageway now marks the site of an assassination attempt on Ronald Reagan that some say broke a 140-year-old curse.

Need a hardcopy of the 50-title Code of Federal Regulations? This is the place.

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

One of the most influential presidents in U.S. history wanted only this plain, elegant monument as his lasting memorial.

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

The little-known, 300-year history of the area includes former lives as a bustling tobacco port, parking lot, and industrial dump.

Senators used to relax in the nearly forgotten marble tubs now hidden in the U.S. Capitol Building's basement.

Before Nixon, "watergate" meant canals.

A historic arena where the Beatles played their first concert in the U.S.

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

Washington's iconic carousel has a nice piece of Civil Rights history.

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

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

Art deco landmark on the outskirts of Washington, D.C.

The oldest building in the District of Columbia was preserved because of a mistaken connection to George Washington.

The monument's pointy aluminum tip has been melted down by repeated lightning strikes.