A rocky sea serpent hides caves, blowholes, and a spectacular natural bridge.

A subterranean playground in an abandoned slate mine.

This unusual 7th-century Frankish seal offers more questions than answers about its past.

This imprint of an old computer keyboard has a unique backstory.

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

This annual harvest parade features intricate floats covered with fruits, vegetables, and seeds.

The spectacular history of spectacles on display.

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

The largest collection of handbags in the world, the oldest of which were used to carry Bibles, primarily by men.

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

This unique sculpture proved invaluable when it saved a train from careening off the tracks.

A retail shop has preserved the 17th-century food cellar from the old building it now occupies.

The house of physicists Paul Ehrenfest was also a temporary dwelling and study for his good friend Albert Einstein.

A relic of the old jail still stands in its original location.

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

This small museum located under the famous cube houses, is home to some 30,000 chess pieces.

Unknown to many, this is where items not displayed in a Dutch history of science museum are held.

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

It's forbidden to dig within this ancient Roman fort hidden beneath a playground.

The portrait of a man from Japan who sent weekly letters to a Dutch hotel he never visited.

A striking memorial to the Jews of Leiden who were murdered during World War II is scattered throughout the city.

Albert Einstein would often sit in this chair during visits to the observatory to discuss science with Willem de Sitter.

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

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