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

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

Cat art as far as the eye can see.

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

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

The world's largest collection of fine-scale miniatures and one the nation's largest collections of antique toys.

The "World's Largest Underground Business Complex," a 55,000,000-square-foot city underneath Missouri.

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

Where the high court feasted, frolicked, and high courtesans put their royal lovers' diamonds to the test.

Walk through spectacular aisles of hanging meat and wagon wheel–sized cheese at the world's largest wholesale food market.

Egyptian Revival movie palace abandoned for decades and restored in 2013.

Down a cobblestone alleyway is a museum dedicated to Romanticism, with a secret garden.

Exquisite wall sculptures carved in secret by an early quarryman in an obscure corner of the Paris Catacombs.

This massive library holds what was once the largest book collection in the world.

An extraordinarily ornate museum in San Diego holds wondrous anthropological treasures.

The 19th-century home of Count and Countess von Hallwyl is now a museum.

Every Tuesday, students let off steam by screaming into the night air.

The single richest source of elemental discoveries in the world.

The internet as provided by a James Bond villain.

Now a hotel, this former bank was the site of a robbery that spawned a psychological phenomenon.

An ancient Viking runestone hidden in plain view in Stockholm's old town.

A hidden bathhouse in one of Stockholm's oldest and busiest neighborhoods is open to anyone who can find it.

Undone by Prohibition, this abandoned brewery-turned-flour mill is now ready for its third act.

Two hundred tons of pioneer artifacts were painstakingly recovered from a shipwreck at the bottom of the Missouri River.