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

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

In the middle of a Vienna square, Roman ruins dating back some 2,000 years are on display.

This series of Baroque passageways in Vienna's cultural center mix old architecture with modern art.

Vienna's diversity-themed traffic lights were inspired by the Eurovision Song Contest.

The Habsburgs' royal collections of art and wonders.

Beautiful Austrian natural history museum with carved ceilings and row after row of ancient taxidermy.

A tropical paradise just a short trip from the opera house is filled with beautiful winged creatures.

The beautiful baroque library of the Hapsburg empire.

Baroque celebration of the end of the Great Plague of Vienna.

The crypt of the imposing Stephensdom holds royal intestines and thousands of skeletons.

The final resting place for the remains of 143 Habsburg royalty.

Mysteriously stacked storefront paths give this medieval British town an iconic style like none other.

The western face was supposedly left clock-less to snub the Welsh.

This stone tower was built to protect Crete from incoming pirates.

A minotaur, a labyrinth, and a dubious restoration pull in visitors from around the world.

This famous archeological mystery may be an ancient example of movable type.

A gruesome and mysterious ancient sculpture of a pagan deity from the Roman occupation of Celtic Britain.

A mysterious shape catches the eye in this 16th-century painting.

This mysterious and unique painting is filled with symbolism.

This macabre painting of a Shakespearean scene looks like something out of a nightmare.

This museum inside a museum tells the story of London's timepieces.

The "lost friend” is the most famous of the six moai statues that were removed from Easter Island.

Kings Cross Station pays tribute to its role in Britain's best-selling book series.