A computer bug so primitive it was an actual insect.

This stately mansion, built in 1787 by America's first Secretary of the Navy, is rumored to be one of the most haunted buildings in Washington, DC.

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.

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

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

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

Government testing at the asylum briefly explored using marijuana as a "truth serum" on Nazi prisoners of war.

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

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.

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

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.

19th-century operating theatre in which the use of ether was first demonstrated - plus, a skeleton and a mummy!

Museum dedicated to awful artwork.

The Boston square dedicated to the dark poet who was born nearby.

One of the oldest used bookstores in the U.S. has been selling antiquarian treasures since 1825.

This Boston medical museum features the skull of the famous medical case of Phineas Gage.

An enormous, inside-out glass globe built in 1935.

This Civil War monument was designed by an eccentric architect and Gettysburg veteran.

This monument marks the beginning journey of a wounded soldier's leg that ended up almost two states away.

Long before the Battle of Gettysburg occurred, dinosaurs roamed the area and left their footprints on this bridge.

One of the last few places in Manhattan that employed a pneumatic systemic keeps it on display.