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

A hidden gem on the lawn of the U.S. Capitol Building designed by landscape architect Frederick Law Olmsted.

A wondrous old library overlooking the nation's capital.

One of the dwarven trees dates back to 1625 and survived the Hiroshima bombing.

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.

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

The United States Capitol's former columns still stand.

With over 100 jam-packed rooms to explore plus elaborate tea services and events, the Mansion on O Street is a hidden treasure.

This ornate Victorian marketplace was the setting for Diagon Alley and the Leaky Cauldron in the Harry Potter films.

The world's largest collection of witchcraft regalia.

The hidden "ballroom" under a mansion lake was built by a criminal who ate a cyanide pill during his trial.

The sign at the garden gate reads: "These Plants Can Kill."

London's creepiest cemetery was once the site of dueling magicians and mobs of stake-carrying vampire hunters.

Nicknamed the "Museum of Horrors," this French anatomical collection has been fascinating visitors for over a century.

Dolls of all shapes and sizes display the eras of femininity in this spooky and beautiful collection.

Inside a former cabaret, seven floors of erotic art.

The celebrated eyesore created by starry-eyed sweethearts.

Weird wax anatomical models reside here, as do other anatomical specimens.

The tomb of a hard traveling saint is constantly covered in shoes as offerings to heal disabled youth.

When the imprisoned pope's remains were finally returned to the Vatican, his heart stayed behind in France.

A unique museum tells the story of the day-to-day life of World War I soldiers.

Supposed home of the camel ridden by Napoleon during his Egyptian campaign.

Before the electric telegraph, a chain of stone towers carried messages across France.