The world of the ancient Celtic civilization explained through a bewitching 11 acre garden.

The ruins of an 800-year-old monastery boasts the tallest round tower in Ireland.

One of the most popular megalithic sites in Ireland stands as a humbler version of Stonehenge.

Ireland's most remarkable collection of these curious cone-shaped houses is worth the buzz.

A proud bronze billy stands as an eternal symbol of Ireland's oldest festival, where a goat is made king.

An important landmark in the history of algebraic logic.

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

This historic Dutch newspaper building is covered with media-themed details—and one unrelated oddity.

The works of poetry's biggest names grace the walls of the city of Leiden, all carefully painted by hand.

Science meets wall art to highlight the beauty of famous mathematical equations.

A former plague hospital turned medical museum.

A massive explosion that leveled hundreds of buildings in the city of Leiden is remembered by a waterside plaque.

Only a few walls remain of the last church the Pilgrims used before they sailed to North America.

A tiny house showcases the busy life of a local gnome.

This century-old street sign is a forgotten remnant of the old city.

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

This 11th-century castle sits so low you can't see it behind the surrounding buildings.

An unassuming rod in the Netherlands was once the old standard unit of length for the entire Dutch empire.

A trio of red, white, and blue stones embedded in the streets of Leiden are markers of medieval territory and law.

One of the great math minds of the 17th century is underfoot in this 900 year old Dutch church.

This disused VLF radio station is no longer in service but the surrounding town still bears its name.

The old observatory in Copenhagen has a spiral corridor used as a racetrack.

A living memorial to the trees London lost during the Great Storm of 1987.

This beautiful deer park was built so King Charles I and his court could go hunting while escaping a deadly plague outbreak.