A haunting tribute to pioneering photographer Clover Adams.

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

You could be standing at the site of one of D.C.'s most fatal tragedies and not even know it.

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

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

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

Cold War intelligence agents monitored communist embassies from an attic in a former pigeon coop.

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

An obscure public service from the U.S. government that redeems burnt, moldy, and soiled old greenbacks.

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

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

Largest Roman Catholic church in North America.

A rotating cast of guys and dolls in front of a Washington, D.C. building.

When it opened during the final years of the embargo, all the drinks and cigars were free.

There’s a hidden military meme engraved on the World War II Memorial.

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

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

People escaping slavery may have hidden inside a corpse vault.

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

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

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

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

A wondrous old library overlooking the nation's capital.

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