Site of one of World War I's most horrific scenes.

A Christian retreat founded to welcome refugees fleeing from the Nazis during World War II.

A 16th-century fountain marks the site of a lost medieval cemetery once filled with mass graves.

The world's most famous cheese caves.

Twelve grave-faced marble angels guard the emperor's tomb at Les Invalides.

Massive puppet-automaton machines created by French artist collective Machines de l’Ile.

This former “ante-chamber to the guillotine” has been refurbished to illustrate the brutal history of French justice.

Hundreds of hidden passageways weave through the old quarters of Lyon.

A grand New York post office that is home to mailman Santas, scraps of postal history, and a pneumatic mail system.

This Manhattan skyscraper is a reminder of the brief but glorious age of urban air taxis.

This anonymous businessman sculpted in bronze became an enduring memorial after 9/11, and had been mistaken by rescue workers for a survivor in the rubble.

The one-time epicenter of American songwriting is now a little remembered Manhattan commercial block.

Lady Liberty's first beacon of enlightenment is now displayed in a museum near the statue.

A dark patch of the ceiling at Grand Central Terminal which was not restored is still stained brown by tobacco.

The most confusing clock in New York.

Every half hour the eye-rolling clock face sticks out its tongue to mock the good citizens of Koblenz.

This historic address is home to the beloved ball and is an almost totally empty building among the most expensive real estate in the world.

Named the fifth most beautiful building in America in 1885, this former courthouse boasts the best view in the Village.

Cryptic messages embedded in the New York City sidewalk.

An uber-secure, windowless tower of doom in the center of Manhattan is an NSA spyscraper.

Though its celestial ceiling is impressive, the true star is the vast collection of French books.

Manhattan’s Battery Park has a whimsical carousel full of spinning, glowing fish.

A popular European tradition makes its way to the states on one of America's most famous bridges.

Wall Street has a new heroine, a bronze statue of a small but fierce girl.