The titular "little arch" near this Italian resort is one of the most popular diving spots in the country.

The world's most active stratovolcano is almost always erupting.

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

A beautiful but toxic fountain of mercury.

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

The most visited, and possibly most controversial, museum in Germany.

Thousands of coffin-like pillars make up this controversial Holocaust memorial.

London's last remaining public soapbox site has seen speeches from Karl Marx, Vladmir Lenin, and George Orwell.

A fake medieval village in the middle of Turin.

A medieval replica of King Arthur's legendary table, the Round Table hanging in Winchester Castle was decorated by Henry VIII.

Böttcherstraße's bells, extolling Nordic virtues and the great conquerors of the world.

The world's largest wooden structure.

Spain's unique Mosque-Cathedral has been a place of worship for both Muslims and Christians throughout its history.

Legacy of the earthquake that nearly wiped Lisbon off the face of the Earth.

This Industrial Age architectural and engineering gem helps visitors and residents alike traverse Lisbon, “The City of Seven Hills.”

Elaborately carved to showcase the glorious wealth that the age of exploration brought to the Portuguese empire.

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

An ancient and majestic fortress that played an integral role in Portugal's road to independence.

This unreal Portuguese palace looks as though it's made from a pile of different castles.

Pilgrimage site for star-crossed lovers.

Synagogue built from the stones of Solomon's temple contains the golem of Prague.

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

A 16th-century Andalusian palace.

Hundreds of lucky felines haunt the ruins where Caesar was murdered.