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

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

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

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.

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

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

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

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

The oldest continuously operating fish market in the United States.

The national park was once a plantation estate.

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

A nostalgic bibliographic gem.

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

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

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

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

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

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

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.

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

People escaping slavery may have hidden inside a corpse vault.

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

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