The prison where Hitler wrote "Mein Kampf," and 278 Nazis were later executed for war crimes.

A graveyard and memorial chapel for victims of leprosy.

This giant middle finger statue sends an unambiguous message to Italy's bankers.

This grisly effigy displays an early Christian martyr who was skinned alive and beheaded.

An ossuary built in 1210 to collect bones from the Ospedale Maggiore of Milan.

Since ancient times these picturesque springs have been providing bathers with healing waters.

This otherworldly French waterfall looks like its waters have turned to stone.

Immortalized by artists, this church incorporates a medieval lighthouse into its shoreside structure.

You would never come across this tiny green oasis if you didn't know it existed.

The compass on its front was a handy tool for 17th-century merchants who needed to know the direction of the wind.

This gruesome biblical parade celebrates the one day a year that a bit of Jesus' blood turns to liquid.

Inside this former medieval prison is a collection of objects designed to inflict unbelievable pain and suffering on the human body and mind.

Christ's blood allegedly preserved in a Belgian town.

A beer pipeline runs beneath Bruges.

You can spot this teeny tiny stained-glass window from the Bonifacius bridge.

Hiding the longest subterranean river known in the world.

A distinctive former power plant turned university lecture hall looks like it could make you breakfast.

This bakery and museum offers tours of the tastes and mythology of Aachen's signature spice biscuit—just don't ask for the recipe.

Incredible labyrinth of man made caves.

Visit the ancient, mysterious Roman catacombs ... in the Netherlands.

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

This historical Netherlands fortress still bears the marks of its single siege.

A luxury hotel housed in a former 15th century Gothic church.

This centuries-old gothic monster has been converted into a sprawling, glossy bookstore.