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

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

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

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.

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

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

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.

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

A wondrous old library overlooking the nation's capital.

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.

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.

This historic New Orleans cemetery is the final resting place of members of the Independent Order of Odd Fellows.

Site of a former hidden treehouse in New Orleans.

The tallest monument in a historic New Orleans cemetery was prompted by romance and dash of pettiness.

An abandoned underground bunker not far from downtown New Orleans.

Once the site of a Native American harvest festival, this humble clearing later played an invaluable role in the birth of jazz.

The beautiful, fruit-covered facade hints at this building's former life.

Parts of the civil rights movement unfolded in this historic eatery, helmed by the "Queen of Creole Cuisine."