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

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

A super-sized promotional trick that is now a D.C. landmark.

A computer bug so primitive it was an actual insect.

An Industrial Revolution-era public work that purified water using nothing but sand.

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

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

The oldest continuously operating fish market in the United States.

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

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

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

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

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

A haunting tribute to pioneering photographer Clover Adams.

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

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

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.

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

Largest Roman Catholic church in North America.

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