Cold War intelligence agents monitored communist embassies from an attic in a former pigeon coop.

There's a crumbling old mansion inside the Smithsonian National Zoo.

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

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

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

The national park was once a plantation estate.

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

A derelict bit of transportation infrastructure hidden in the woods.

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

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

A monument in Washington D.C. marks the spot from which all other roads were supposed to stem.

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

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

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

Home to items never before seen by the public.

The site of the climactic scene from the classic horror film is now a historic landmark.

The United States Capitol's former columns still stand.