Nearly 40 miles and 1,000 years of limestone mines under Denmark.

This Danish rock field is actually a sprawling ancient cemetery holding the bodies of 700 Vikings.

Beneath Denmark's Højbro bridge, a bronze merman and his seven sons forever mourn for the mother and wife who left them for land.

An enormous playhouse designed to look like 21 stacked Lego bricks, with another 25 million colorful Legos inside.

A 1,215-foot tunnel transports pedestrians beneath the River Thames.

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.

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

A tongue-in-cheek arcade where the games are based on everyday life.

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

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

This collection of illusory paraphernalia has been culled from the history of London's premier magician's club.

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

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

This shop and gallery is a modern-day cabinet of curiosities, unassumingly positioned along an urban thoroughfare.

One of the few remaining casualties of the London Blitz, this destroyed church has become an enchanting public garden.

Opulence and fantasy collide in this royal chair which is supposedly made with unicorn horns.

Six beautiful wooden giants are hidden around Copenhagen.

Pre-Nazi swastikas adorn the sculpted pachyderms flanking this brewhouse portal.

A walkable map of the world, made from soil and stone by one man.

Copenhagen's celebrated theme park and gardens.

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

A series of modernist treehouse hotel rooms grace the outskirts of an Arctic forest.

The library's graceful rotunda is like a bibliophile's temple.