This Polish cave has housed a dragon, a brothel, and an enduring legend.

The former Nazi concentration camp stands as a museum to remember this dark chapter in European history.

An underground city of salt.

Built in 1870 at the bridge that connected Buda and Pest, this spectacular incline railway was almost lost forever during World War II.

Two stone columns flank the grand Venice square, but there were supposed to be three.

Thousand-year-old Viking runes adorn an ancient Greek lion at the entrance to the Venetian Arsenal.

Go inside to really appreciate this 500-year-old technological masterpiece.

This 2,000-year-old Doric bridge is still open to pedestrian traffic to this day.

Ruins of a German Castle on top of a towering stone pillar.

A monument to the three wars that led to German unification towers within a Berlin traffic circle.

This strategic isle was once swapped between empires and almost entirely destroyed in a bomb explosion.

This Dresden church was purposely rebuilt Protestant after being demolished in World War II.

The bells remain in a shattered heap exactly as they fell when the church was bombed in World War II.

A memorial to a Swedish hockey player's "encounter" with aliens.

A whimsical sculpture garden right out of a children's storybook.

The deepest metro station in the world.

When you've got to go, you've got to go.

340-foot statue built to honour the Heroes of the Soviet Union.

It houses the remains of a 17th-century version of the Titanic.

A marvel of Byzantine engineering under the streets of Istanbul.

A king's pet, a pope's gift, an artist's inspiration, and a tragic shipwreck.

Despite attempts by local police to discourage it, Beatles-inspired graffiti has been a means for artists to air grievances for decades.

This bridge was constructed from the rubble of the infamous Bastille.

Six ravens are kept captive (but well-fed) at the Tower of London to prevent the fall of the Crown.