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

Before Metro, Washington had a robust streetcar network—and you see the remains of this infrastructure if you know where to look.

100 years later, they're still down there.

The first presidential bomb shelter was located in an old vault under the Treasury, connected to the White House via tunnel.

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

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

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

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

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

Helen Keller once broke ground on this historic center for the study of technologies to benefit the hearing impaired.

A historic estate packed with George Washington's heirlooms, and its own nuclear bunker.

A historic neighborhood church is reborn as a psychedelic arts collective.

The famous abolitionist’s preserved estate is one of Washington's finest monuments to its great Black citizens.

An atomic bomb-proof strongbox protects the U.S. Constitution from terrorists and thieves.

Housing the National Women's Party since 1929, this historic house is now a monument to the fight for gender equality.

The beloved statue at the National Academy of Sciences is oh so inviting to sit on.

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

A painfully obvious spy house sits right across the street from the Russian Embassy.

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

This leafy estate is worth $18 million and is so grand it has two mailing addresses.

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

This lonely waterfront memorial to the men of the Titanic was erected by the "Women of America."

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 nostalgic bibliographic gem.