The popularity of Sherlock Holmes led to the creation of his fictional address, turning the orderly London street numbers askew.

The second-largest cave chamber in the world was discovered in 1898 by a 16-year-old and a friend known as "Pothead."

A fantastic castle rumored to be the birthplace of King Arthur.

A church that bred legends, and served as an inspiration for the Da Vinci Code.

Ruined 11th century abbey built by King David I in Edinburgh, Scotland.

This ornate Victorian marketplace was the setting for Diagon Alley and the Leaky Cauldron in the Harry Potter films.

The celebrated eyesore created by starry-eyed sweethearts.

360° views of the city plus five floors of optical illusions and hands-on science.

The world's longest known cave system.

The gloomy ruins that inspired Bram Stoker to bring Dracula to life.

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

Pompeii's less famous neighbor is still revealing her secrets.

17th century streets hidden under Edinburgh were once a breeding ground for the black death.

France's most famous cemetery, with some of its most curious tombs.

Famously misunderstood wonder of the ancient world

This 1,300 year old monastery built atop a single rock was once only accessible depending on the whims of the tide.

Macabre astrological automaton clock dating to the late 1400s.

A church of bones, decorated with 40,000 human skeletons.

London's creepiest cemetery was once the site of dueling magicians and mobs of stake-carrying vampire hunters.

The vast, legendary catacombs hold secrets much stranger than stacked bones.