Castle and secret tunnel withstood a siege until its owner was killed by the Holy Roman Empire, while sitting on the toilet.

The Origin of On the Origin of Species.

The handiwork of a underdog clockmaker who solved an impossible problem for an Empire, and forever revolutionized seafaring.

William Buckley escaped from prison and is said to have spent years hiding in this seaside cave.

This curious fresh and salt water lake holds a secret that draws in deep divers from around the world.

Obscure Freemasons still live in D.C.’s largest private residence.

One of the only places where Earth’s mantle lies above water.

Recognized the world over as the home of the McCallisters in the 1990 movie "Home Alone."

Despite many attempts to finish this overpass, it has been abandoned since the 1970s.

A measuring mishap led to these artificial stone ladies losing their stomachs.

This gracefully curving formation looks like a massive wave that was suddenly turned to stone.

This once-booming gold mining hub was basically abandoned overnight.

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

This bridge was constructed from the rubble of the infamous Bastille.

The subterranean "lake" below the Paris opera house inspired the Phantom of the Opera's lair.

Got apples?

A subterranean shelter remains intact under a busy Paris railway station.

A favorite Paris bar for U.S. expats, including Gershwin, Hemingway, and James Bond.

Down a cobblestone alleyway is a museum dedicated to Romanticism, with a secret garden.

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.

Paris' linguistic guide to the international language of, yes, love.

This surreal statue brings a famous French novel about a supernatural cad to arresting life.

Ancient ruins hidden underneath a modern luxury hotel.

Gods clash with machines in a power plant regenerated as a museum.