A plaque hidden in the law faculty at Leiden University honors the first scientist to make liquid helium.

One of the oldest masonic temples in the Netherlands, built in 1757.

The remnants of a WWI naval mine that once terrorized the country now decorates a street.

Once housed in the towers of this Gothic church, this 17th century clock still ticks today.

One of the Leiden's oldest pubs is also the birthplace of the Heineken star.

Now a museum, this building was once a 14th-century monastery and the place where the founder of the Dutch nation lived and was assassinated.

The grave of the famous painter is marked by a simple stone in the ground.

The oldest-known example of a historic architectural style recognized by UNESCO.

Macabre symbols of death and mummies on display set the tone of this Italian purgatory church.

The Bloemen Route, or “Flower Route”, stretches 25 miles through prime Dutch tulip country as a result of “tulip mania,” the world’s first economic bubble.

A preserved building where the dead were once watched for signs of life.

Dramatic sea stacks adorn the coast of this small village on the Adriatic coast.

A 1,000-year-old church holds the bones of the Christian martyrs who died hiding inside it.

This 10th-century seaside abbey holds spectacular views and a window into the past.

It's believed that these columns marked the end of the Via Appia.

A long-buried ancient ruin unearthed right in the middle of the city.

One man's quest to fix his toilet unearthed over 5,000 artifacts spanning more than 2,000 years of history.

The sunlight passing through the opening of this huge cave system creates a magical effect.

Southern Italy's spinning top village.

Geometry and mystery come together in an epic show of octagonal masonry.

People have been living in the cave houses on this Italian hillside since the Neolithic era.

Skulls and skeletons are omnipresent in this church dedicated to souls trapped in purgatory.

An abandoned quarry hides an open-air gallery of huge sculptures, some made from the rubble of 9/11.

An impressive bridge over a ravine also served as an aqueduct.