This medieval Italian town is a sheer (and beautiful) cliffside defense.

One of several skulls claiming to belong to the beheaded St. John the Baptist is on display at this Roman church.

This ritzy Italian market is built around a statue of an unforgiven heretic who was burned for his belief in an endless universe.

The skull of the patron saint of lovers lies in the Basilica di Santa Maria in Cosmedin—maybe.

The doodles of a genius line the walls of a secret room under the Medici Chapel, where they were hidden for nearly 500 years.

The yawning maw of this pagan visage is said to bite off the hands of liars.

Rome's semi-secret peephole vista is also a former Crusader stronghold.

Amsterdam's former hotspot for public executions and dissections.

This gorgeous reading room houses the oldest and largest art history library in the Netherlands.

A floating cat sanctuary on an Amsterdam canal.

Museum preserving torture methods from the past.

The world's only museum devoted to the wonders of fluorescence.

Trek up this glacier before it disappears.

The birthplace of the ferocious William the Conqueror, this castle is awash in medieval history.

Dedicated to the history and culture of smoking, this small museum now includes a vape lounge.

The historic Masonic Lodge in which the first-ever female Mason was initiated.

Nicknamed the "Museum of Horrors," this French anatomical collection has been fascinating visitors for over a century.

A French library that makes sure its love of books is writ large... giant in fact.

An iconic and eccentric bar for "Manouche" Jazz music keeps expanding its space—and its influence.

The spiral staircase hidden inside this giant Parisian column was likely built for Catherine de Medici's astrologer.

Beggars were miraculously "cured" of their fake ailments when they returned home to this 17th century Paris slum each night.

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

This museum in a Paris apartment gives a unique look at the iconic French singer's life.

Monsters and miniatures are held in equal esteem at this wondrous museum.