One of the largest caves in the world open to the public.

During World War II, this rice mill became a Nazi concentration camp.

When a massive landslide hit one of the world's tallest dams it created a tragic environmental disaster.

A star-shaped fortress town fort built in the geometric model of the Renaissance utopian city.

This shining multicolored metro station deep under Naples is said to be the most beautiful in Europe.

This influential Renaissance-era library was once the haunt of kings and monks.

The final resting place of the great navigator, or maybe his brother.

Spanish architects used seized Muslim gravestones to rebuild parts of the fortress.

A curious carving hides on a marble column in the Mosque-Cathedral of Córdoba.

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

Giant topiary dog once played a role in a terrorist bomb plot.

Historic medieval fortified city in southwest France.

A medieval church with largest and oldest collection of Renaissance frescoes in France.

This ancient theater was once the home of fierce gladiatorial battles.

Ernest Hemingway was the first to sign this colorful wall covered in thousands of celebrity signatures.

The location of the last witch trials of Italy, known as "The Salem of Europe."

This statue of the great Argentinian car driver is located near a famous curve of the Monaco Grand Prix.

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

This massive collection of British military artifacts includes the heartbreaking personal letters of the men in the trenches of WWI.

Thanks to modern navigational tools we now know that the true prime meridian runs through a park next door.

Scattered throughout London are ancient remnants of the city's former bounding wall.

Hear the quietest sound from across the dome.

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

Eighty million natural history specimens call this gargantuan museum home.