This impressive Boston holy house is the American mecca for Christian scientists.

Two thousand artifacts from around the world collected by one woman who loved to travel.

A beautiful but toxic fountain of mercury.

An "inside out" building in the historical center of Paris, featuring Europe’s largest modern art museum.

Noirish green neon marks the location of one of the oldest private detective agencies in France.

The water-powered carriages are long gone, but for over a century this funicular railway has been the fastest route to the highest point in Paris.

A French museum of wrought iron.

The man who introduced reinforced concrete to the world demonstrated its genius by using it to build his own house.

An ancient ossuary in Rouen.

Home to the "Rat King" of Nantes and other wonders of the natural world.

With a history of slaughter, feast, and famine, remnants of the pork industry decorate this area--even its church.

The headless bodies of more than 1,300 guillotined victims of the Reign of Terror are buried here in mass graves.

A haunting collection of the vanished and disappearing natural world.

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

Walk upon the mementos of the dead in this Parisian courtyard paved with medieval tombstones.

Notorious artist squat renovated into legal studios.

If they push on just the right spot, even the weakest person can move this titanic boulder.

The spiral staircase hidden inside this giant Parisian column was likely built for Catherine de Medici's astrologer.

Known as the "Dodo Manège," this carousel features a herd of animals that have disappeared—or may be gone soon.

Hidden away in a modern library are the remains of one of the 18th century's most celebrated wunderkammers.

A colossal sculptural lion built by the same man who designed the Statue of Liberty.

A king's pet, a pope's gift, an artist's inspiration, and a tragic shipwreck.

Legacy of the earthquake that nearly wiped Lisbon off the face of the Earth.

This Industrial Age architectural and engineering gem helps visitors and residents alike traverse Lisbon, “The City of Seven Hills.”