An overlooked oasis of quiet on the grounds of Washington's monumental basilica.

The span is crooked and made from two older recycled bridges.

For 60 years, the academy had no permanent location until members voted Washington D.C. as its forever home.

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

D.C.'s first central library was born out of a chance encounter with the philanthropist whose name it bears.

The hidden offices underneath Memorial Bridge have been locked up since 1976.

A hoard of sky catalogs, astrophysical journals, even the works of Galileo and Copernicus.

This imposing Masonic temple a mile from the White House was the first public library in Washington, D.C.

There's a crumbling old mansion inside the Smithsonian National Zoo.

Home to a vast and influential collection of Shakespeareana.

Government testing at the asylum briefly explored using marijuana as a "truth serum" on Nazi prisoners of war.

The national park was once a plantation estate.

The walls of the iconic dome are hollow and have a secret stairway.

The oldest continuously operating fish market in the United States.

The Byzantine, pre-Columbian, and medieval art at this stately mansion are some of the most under-appreciated collections in D.C.

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

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

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

A derelict bit of transportation infrastructure hidden in the woods.

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

A cavernous three-story, 43,800-square-foot basement that was forgotten about for 60 years.

Enormous piles of historically significant stones, dumped by Congress in a forest, and abandoned for 60 years.

This grand gothic brewery has been pumping out suds for over a hundred years.

A wondrous old library overlooking the nation's capital.