A floating cat sanctuary on an Amsterdam canal.

The world's first zoo for microbes collecting the horrible and wonderful things living on and around us.

For over 100 years the most important physicists in the world have autographed this university wall.

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

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

This early 19th-century graveyard is the final resting place of Vincent van Gogh's mother.

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

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

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

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

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

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.

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

Once the world's biggest telescope, it was later used as a coat hanger by a famous Dutch astronomer.

People have been placing babies on these lilies for photoshoots since the Victorian era.

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

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

The remains of a medieval wall discovered in the basement of a jewelry store.

This public library and its impressive collection of academic books have not changed since the 17th century.

This small museum collects the Christian remembrances which would otherwise be forgotten.

Graffiti covers the walls of a room where university students through the centuries have waited nervously to defend their theses.

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.