A historic London pub with prison cells in the cellar and a "spy room" on the second floor.

An unusual round church in London with a Templar past.

This London pub hides a peculiar secret: a recreation of the rooms shared at 221b Baker Street by Sherlock Holmes and Dr. Watson.

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

This memorial to World War II's fallen airmen shows us the movements of the stars that once guided them.

The little-known second castle that William the Conqueror built in York.

The National Railway Museum in York is the largest railway museum in the world, attracting almost 1 million visitors per year.

This network of narrow, medieval passages has the most delightful name.

These steps offer a breathtaking view of one of Europe's most besieged fortresses.

Scotland still bears an enormous scar of its Roman past.

Above an abandoned Underground station, this charming bookstore is home to strange antiquities and literary works.

The de facto symbol of Copenhagen is this bronze fairytale which cannot seem to keep its head for very long.

Copenhagen's celebrated theme park and gardens.

A vast overgrown cemetery, once known as one of London's "Magnificent Seven."

The curious underground history of keeping Paris clean.

A museum on the history of Paris, including a set of Napoleon's toiletries, Proust's room, and relics of the Revolution.

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

One of the oldest medical collections in Europe focusing on rare surgical instruments.

The oldest stone house in Paris was built by its most famous alchemist.

The quaint little store that is said to have inspired a famous Dickens novel was only given its name after the book was released.

Rebuilt remains of a temple to Roman god Mithras.

The only university zoological museum in London houses extinct animals, bizarre natural history specimens, and a Micrarium of microscopic creatures.

The spot where three Protestant clergymen were burned at the stake during the reign of "Bloody Mary."

A stone copper was sculpted on the wall of the Carlisle Cathedral to honor a local hero.