The shared home of a utopian commune that practiced "free love" a century before the hippies.

This plaque in one of London's oldest public hospitals commemorates the first meeting of two of Britain's most famous literary heroes: Sherlock Holmes and Dr. Watson.

One of the world's largest collections of pathological specimens.

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

The oldest stone house in Paris was built by its most famous alchemist.

This massive library holds what was once the largest book collection in the world.

This off-limits room in the National Library of France is home to a system of pneumatic tubes, once used to bring books to readers.

The history of radiation is on safe display at the foot of a radiation science laboratory.

Mile-long cave system near Great Smoky Mountains.

The remains of the iconic train crash from the movie The Fugitive can still be found rusting along the Great Smoky Railroad.

An abandoned asylum where patients have been forgotten but their possessions remain.

An abandoned asylum once on the cutting edge of lobotomies may be reborn as a Christian college.

An abandoned tuberculosis hospital moulders on into an uncertain future.

A beautiful, historic location open to the public.

Now a retreat center for the faithful, it once provided training for clergy—but it began as a farm owned by a famed financier and his opera singer wife, who built a surprise in the backyard.

Home to the infamous "Typhoid Mary" and the worst loss of life in New York's history prior to September 11, 2001.

Nikola Tesla's former home contains an homage hidden from plain sight.

A quiet memorial marks the spot where the victims of the Salem Witch Trials were executed.

The remains of a hospital ravaged by fire, once a progressive place of innovations for disabled children.

The world's only surviving heavy cruiser has a haunting history.

Connecticut grave of the woman responsible for the Winchester Mystery House in California.

Piano-making empire filled with 200-year-old steam machines still churning out 1,000 instruments a year.

A charming "tea atelier" hidden away in Greenpoint, Brooklyn.

A Ukrainian church canteen doles out hearty fare in an East Village basement.