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

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

Four bald cypress trees in Lafayette Square, across from the White House, mark the southern edge of a 100,000 year old cypress swamp.

A wondrous old library overlooking the nation's capital.

‘Bush the old fire dog died of poison July 5th, 1869. RIP.’

The first purpose-built art gallery in the United States is once again open as a center of craft arts.

This sandwich shop has a century-old elevator behind a sheet of plexiglass.

This stately mansion, built in 1787 by America's first Secretary of the Navy, is rumored to be one of the most haunted buildings in Washington, DC.

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

Home to a vast and influential collection of Shakespeareana.

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

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

It was once the base for a series of domestic terror attacks.

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

Rumor has it the uncarved lump behind the three famous suffragists is reserved for the first woman president.

A fantastic array of trays and cables once whisked books over to the Capitol at 600 feet per minute.

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

These recently uncovered walls are all that's left of Washington, D.C's first defense contractor.

A museum cafe showcases Native American dishes and indigenous ingredients from across the Western Hemisphere.

A computer bug so primitive it was an actual insect.

The most decorated dog of World War I is preserved in the Smithsonian.

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

The actual model from the original "Star Trek" series is now on display at the National Air and Space Museum.

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