The privately owned cemetery that holds room for Washington's finest when they step down from life.

The hidden offices underneath Memorial Bridge have been locked up since 1976.

A celebrity from the late Cretaceous period.

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

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

The national park was once a plantation estate.

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 derelict bit of transportation infrastructure hidden in the woods.

People escaping slavery may have hidden inside a corpse vault.

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

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

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

During the Industrial Revolution this “Temple of Invention” was full of intricate miniature machines and gadgets.

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

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

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

A wondrous old library overlooking the nation's capital.

One of the dwarven trees dates back to 1625 and survived the Hiroshima bombing.

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

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

Home to items never before seen by the public.

Pick up all of the cosmic knick-knacks under the sun or take a creative writing course, all offered in this novelty storefront.

A community gathering place that once housed half-ton tanks and the World's Fair.