Cat art as far as the eye can see.

This unattributed sculpture in Amsterdam is hiding in plain sight.

An Amsterdam street lined with antique shops each one dedicated to a different obscure collection.

This collection of 20th-century toys is filled with a lifelong personal toy collection brought from the U.S. to Amsterdam.

The attic of a four-century-old canal house hides a clandestine church.

Amsterdam's former hotspot for public executions and dissections.

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

The history and future of cannabis.

A museum of magic with a Sadist past.

Natural history museum celebrating biodiversity with a parade of taxidermy animals.

A haunting collection of the vanished and disappearing natural world.

The history of radiation is on safe display at the foot of a radiation science laboratory.

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

Known as the "Dodo Manège," this carousel features a herd of animals that have disappeared—or may be gone soon.

This museum houses an imposing skeleton army comprised of creatures great and small.

A melancholy jester sits on the grave of a famous 20th-century ballet dancer and choreographer.

A horde of stray cats rule in this secluded Parisian cemetery under a bridge.

A magical, macabre wax museum, beloved by locals, uses real artifacts to depict an assassination from the French Revolution.

In the best of all possible worlds, everyone will get a chance to see this statue in which Voltaire's heart is interred.

The subterranean "lake" below the Paris opera house inspired the Phantom of the Opera's lair.

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

Statue of death tucked in the University of Medicine courtyard.

The approximate spot where the last Grand Master of the Knights Templar was put to death.

If you look closely at the oldest bridge in Paris, you might notice hundreds of ugly faces leering from its sides.