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

Rumor has it the uncarved lump behind the three famous suffragists is reserved for the first woman president.

A computer bug so primitive it was an actual insect.

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.

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

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

A haunting tribute to pioneering photographer Clover Adams.

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.

The most decorated dog of World War I is preserved in the Smithsonian.

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

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

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

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

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

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

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

The country's oldest continually-operated mini golf course lies hidden in plain sight, eclipsed by one of D.C.'s most popular tourist attractions.

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

A nostalgic bibliographic gem.

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