The ruins of this Dutch castle sit atop a labyrinth of once-secret tunnels and passageways, dating back over 900 years.

Europe's official "zero-level," the equator of elevation.

Oldest Museum of the Netherlands is a true cabinet of curiosities.

A poignant museum dedicated to the history of the Dutch resistance against Nazi occupation

A unique collection of gilded age mechanical pianos.

An overgrown and largely forgotten cemetery lies hidden within the outskirts of Amsterdam.

Ancient catacombs form the foundation for this Rococo orgy of a church.

The stunning interior of this Gothic church is covered in ornate gold details.

A miniature city, once ruled by the Queen of the Netherlands.

Remains of Roman amphitheater hidden in a sleepy quarter of Paris.

A Parisian exterminator's shop whose storefront displays stuffed rats hanging from traps.

A majestic lion statue guards this Parisian botanical garden, and feeds on an unsettling item.

A museum on the history of Paris, including a set of Napoleon's toiletries, Proust's room, and relics of the Revolution.

Indents in the pavement are all that remain from a grisly death machine in Paris.

This statue was given to France by the United States to commemorate the centennial of the French Revolution.

This large copper bolt represents the benchmark for measuring sea levels in most of Europe.

Tucked in the back of a flower shop, its collection details the fascinating history of the Netherlands's iconic symbol.

This museum housed in a former brothel explores the past and present of sex work in Amsterdam.

This cheese shop also houses a museum devoted to Dutch dairy.

Famed for its pie, this eatery has a hidden tunnel that allowed Catholics to secretly walk to church during the Reformation.

A rare tour of an aristocrat's private home reveals valuable 17th-century paintings from artists like Rembrandt.

This bird-loving brewery is situated in an old municipal bathhouse, nestled beside a 300-year-old windmill.

An ancient passage filled with stalls selling used books, once frequented by Vincent Van Gogh.

A curious collection dedicated to human and animal anatomy and pathology.