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

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

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

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

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

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

The remains of Martha, the last known passenger pigeon, serve as a tool to educate about conservation.

The privately owned cemetery that holds room for Washington's finest when they step down from life.

The most accurate timepiece in the world.

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

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

The house where John Wilkes Booth conspired with his co-conspirators.

Largest Roman Catholic church in North America.

The oldest continuously operating fish market in the United States.

The national park was once a plantation estate.

This stunning blue and gold room changed cities twice before becoming part of the Smithsonian.

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

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

The country's oldest continually-operated mini golf course lies hidden in plain sight, eclipsed by one of D.C.'s most popular tourist attractions.

A hidden gem on the lawn of the U.S. Capitol Building designed by landscape architect Frederick Law Olmsted.

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

Fittingly, America's museum of architecture is itself a magnificently designed old building.

A lovely aquatic park built by a one-armed Civil War veteran who made a fortune from lotuses.

A monument in Washington D.C. marks the spot from which all other roads were supposed to stem.