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

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

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

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

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

The oldest continuously operating fish market in the United States.

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

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

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

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

A computer bug so primitive it was an actual insect.

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

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

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

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

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

A haunting tribute to pioneering photographer Clover Adams.

Largest Roman Catholic church in North America.

A Spiritualist house of worship where believers communicate with the dead in the spirit world.

People escaping slavery may have hidden inside a corpse vault.

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

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

A Civil War fort in the middle of Washington, D.C. has been swallowed by a forest.

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