Hidden beneath the streets of London is a secret subway that only carried mail.

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

This cemetery features modernist statues as strange as its name.

These secluded and abandoned anti-aircraft defenses have become one the most scenic viewpoints in Barcelona.

Gaudí's famously flamboyant architectural style is on full display in this sprawling park and garden.

A beautiful but toxic fountain of mercury.

One of Antoni Gaudí's most classic buildings is well-known for its "dragon-back" design.

This former Baroque palace on the historic Calle Montcada is a rare architectural gem and was once the meeting place of an aristocratic scholarly society.

The oldest giants in Catalonia are now displayed in a 14th-century Gothic church.

Banksy gives themself artistic license with this piece of London street art.

High-end antique collection housed in a centuries-old church.

This churchyard arbor is surrounded by hundreds of gravestones placed there by author Thomas Hardy.

This South London cemetery holds the remains of more than 15,000 people.

Claiming to be the oldest hat store in the world, this historic haberdashery had a hand (and a head) in the creation of the Bowler.

The perfectly preserved underground rooms where Churchill plotted the war against Germany.

The broken skateboards that became a poignant memorial to a murdered skater.

This Parisian fountain is a little bit fantasy and a little bit nightclub.

The water-powered carriages are long gone, but for over a century this funicular railway has been the fastest route to the highest point in Paris.

Theme park featuring miniature replicas of European monuments.

Climb inside an iron crystal magnified 165 billion times its normal size.

Meet the bronze beloved pet to a family of famous peeing statues.

Brussels' favorite peeing boy has a sister.

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

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