The scuba diving training facility was named for the steam that rises from the cave's chimney.

A mysterious castle built as a monument to lost love.

A promising candidate for the lost rock laid by George Washington was unearthed, but the hunt is still on.

A derelict bit of infrastructure from the canal that once ran through D.C. is landlocked in the heart of the city.

Before founding the American Red Cross, Clara Barton had a tremendous humanitarian impact by locating thousands of missing soldiers.

This unacceptably tall building was the real reason for Washington, D.C.'s skyscraper ban.

The only National Monument ever to go missing for nearly 50 years then resurface in a dump.

A brass plaque dedicated to a convicted cannibal hangs in the National Press Club, and that's not even the craziest part of the story.

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

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

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

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.

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

An elaborate memorial to a man local legend says died of a broken heart.

A beautiful multicolored mound formed by the mineral deposits of the Orenda Spring.

If you were standing here on October 5th, 1950, you'd be dead.

A mysterious, abandoned building rotting on the Brooklyn waterfront.

A CT scan revealed the identity of this 3,000-year-old mummy that everyone erroneously thought was female.

Adherence to strict Jewish laws is required to enter this ultra-conservative New York village.

A 9-story, poured concrete structure which was used as a glue factory with an indelible smell.

A towering cemetery monument honors a man who threatened to expose the Freemasons and paid with his life.

A near tragic event on this bridge helped inspire the classic film "It's a Wonderful Life."

A young woman's senseless murder led to the controversial psychological theory of the "bystander effect."