France's national museum of scientific and industrial instruments.

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

Northern Ireland's Brobdingnagian stepping stones.

Perfectly preserved ancient monastery in an impossibly dramatic location on a rocky island in the Atlantic.

This medieval castle overlooking the Elzbach river looks just like it did hundreds of years ago.

Spend the night in this formerly abandoned traditional Scottish village.

A botanically themed auditorium blooms within the world’s last operating double-decker theater.

This fantastical waterfall is hidden in a cave located in a cracked cliff.

The atmospheric road was never meant to be so creepy.

Famously misunderstood wonder of the ancient world

Catacombs turned marketplace.

A counter-culture bookstore like no other hides in plain sight in the streets of Paris.

One of the oldest scientific gardens in Britain, containing more than 13,302 plant species in its core collection.

This semi-secret storybook hedge maze is also the oldest garden in the city.

Cat art as far as the eye can see.

The hidden lair of an alchemist rediscovered in a 2002 flood.

Countless grotesque faces stare out from this eerie Prague art wall.

Established in 1638 to battle the Black Death, Hortus Botanicus Amsterdam is a treasure trove of rare flora.

Construction of Barcelona's iconic (but controversial) church is expected to be completed in 2026—a century after the death of its architect.

A Jenga-style cylindrical tower of books that appears to go on forever.

The unique waterfall in Iceland's south features a backdrop of geometric black lava columns.

The sign at the garden gate reads: "These Plants Can Kill."

A floating cat sanctuary on an Amsterdam canal.

This hidden Art Nouveau courtyard is an opulent feast for the eyes.