The commemorative stone column conceals a secret laboratory.

The little-known second castle that William the Conqueror built in York.

“And the Lord said unto Johan, build for thee an ark for the end of the world is approaching.”

Birthplace of the "Cat in the Cradle" and a cluster of iconic, original windmills that let the Dutch tame the seas.

From afar it looks like someone's hat blew into the water, but closer inspection reveals a giant floating sculpture.

An enormous Polaroid picture adds an artistic flair to Rotterdam.

A giant floating rubber duck-bunny painted with a different design every year.

A strangely curved lamppost stands tall over this avenue in Rotterdam.

A nearly 25-foot concrete sculpture of Sylvette, Picasso's muse.

Four giant movable street lights decorate this modern Rotterdam square.

A huge teapot illuminates a home for the elderly.

A modern reimagining of a medieval city gate.

This charming pup is meant to celebrate the youth and stubbornness of the city's students.

A dramatic art installation features a BMW flying out of a building in Rotterdam.

Built by crowdsourcing, this wooden foot bridge saved a part of Rotterdam that was languishing in wait of city funding.

A statue of the second-tallest Dutchman in history.

Old ships and machinery fill a historic harbor in the city that's home to Europe's largest port.

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

This public toilet built in the famous Amsterdam School architectural style is a Dutch national monument.

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

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

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

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

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