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 national park was once a plantation estate.

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.

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

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

People escaping slavery may have hidden inside a corpse vault.

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

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

A nostalgic bibliographic gem.

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

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

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

A historic neighborhood church is reborn as a psychedelic arts collective.

There's a 12-foot-tall replica of the Washington Monument hidden under a manhole nearby.

This grand gothic brewery has been pumping out suds for over a hundred years.

Franciscan monks created a facsimile of the Holy Land for North Americans who couldn’t afford the trip overseas.

Long-abandoned trolley tunnels just a mile away from the White House are turning into an art space.

With over 100 jam-packed rooms to explore plus elaborate tea services and events, the Mansion on O Street is a hidden treasure.

The United States Capitol's former columns still stand.

Home of Dutchy, an exhumed Confederate statue that was once torn down by an angry mob for looking stupid.