The oldest continuously operating fish market in the United States.

A traveling postal dog covered 48 states and more than 140,000 miles, and he lives on as taxidermy, patched up with a rabbit's foot and a pig's ear.

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

The "lovely red Vega" of the legendary record-settling pilot.

Light bulbs, scrap wood, and tinfoil comprise this homemade throne of the gods.

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.

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 hidden military meme engraved on the World War II Memorial.

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

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

People escaping slavery may have hidden inside a corpse vault.

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.

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

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

Largest Roman Catholic church in North America.

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

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

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.

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

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