A secretive collection featuring objects that were designed specifically for U.S. intelligence operations.

This suburban house is made of dirt, and almost sparked a revolution in home construction.

Parking garage where Bob Woodward met Watergate source "Deep Throat."

The national park was once a plantation estate.

These recently uncovered walls are all that's left of Washington, D.C's first defense contractor.

Once home to seven different roller coasters, Glen Echo has undergone many transformations since its founding in 1891.

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

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

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

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

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

Home to items never before seen by the public.

A fantastic array of trays and cables once whisked books over to the Capitol at 600 feet per minute.

America's Most Wanted's set resides in this tribute to the history of crime and punishment.

Go take a picture with the inventor of the daguerreotype photographic process.

Members of Congress have traveled between the buildings on Capitol Hill for a century hidden from tourists, press, and storm clouds.

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

The sci-fi villain is a little-known inhabitant of the U.S. capital's largest cathedral.

A tiny piece of the Moon is embedded in this stained glass masterpiece.

Eighteen miniature death-scene dioramas.

The United States Capitol's former columns still stand.

The shelves in the back of this thrift store are devoted to saving, not selling, retro tech.

The man who first patented the Ouija board rests in peace beneath a headstone that playfully reflects that achievement.

The wooded estate of the Forest Service employee responsible for D.C.’s cherry blossom trees.