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

This banal Parisian entranceway is not what it seems.

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

A series of abstract, silly sculptures represent the works of a great modern classical composer.

The vast, legendary catacombs hold secrets much stranger than stacked bones.

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.

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

The narrowest street in Paris.

This iconic Parisian bookstore doubles as the "Tumbleweed Hotel" for traveling writers.

This churchyard arbor is surrounded by hundreds of gravestones placed there by author Thomas Hardy.

Scattered throughout London are ancient remnants of the city's former bounding wall.

This secret garden has bloomed into London's most unique hub of urban creativity.

Spitalfields' regal market goat is said to be a monument to the area's migrant population but most are pretty sure it's just a goat.

Tucked away in the Tower of London is the weapon once used to execute high-profile prisoners.

Six ravens are kept captive (but well-fed) at the Tower of London to prevent the fall of the Crown.

Graffiti from the 16th and 17th centuries cover the walls of this part of the Tower of London.

One of the few remaining casualties of the London Blitz, this destroyed church has become an enchanting public garden.

The library houses an incredible collection of some of the world's most impressive books and manuscripts.

19th-century scientists would make the pilgrimage here to verify the precision of their measuring sticks.

Thanks to modern navigational tools we now know that the true prime meridian runs through a park next door.

A 1,215-foot tunnel transports pedestrians beneath the River Thames.

This massive collection of British military artifacts includes the heartbreaking personal letters of the men in the trenches of WWI.

An easily overlooked stretch of ornate window fronts and gaslight lamps that could be right from the pages of Dickens.

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