This artificial ring island was built to hold cubic tons of polluted dirt.

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 struggle of a small Dutch island against the sea.

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

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

Where royalty waits in the height of luxury.

Debatably clever, or just plain honest hotel advertised as "The Worst Hotel in the World."

A hidden church in a hidden courtyard tells the story of the Miracle of Amsterdam.

Amsterdam's former hotspot for public executions and dissections.

Famed for its pie, this eatery has a hidden tunnel that allowed Catholics to secretly walk to church during the Reformation.

Occupied for six centuries by Franciscan Order nuns, this monastery is an amazing ode to Catalán Gothic architecture.

This impressive former palace contains a hidden gem for fans of modern sculpture.

The fragmented remains of a massive public bath connected to the city's water supply.

A wonderful collection of fossilized dinosaurs and other creatures that roamed the landscape millions of years ago.

Fascinating exhibits of prehistoric and ancient artifacts displayed with a uniquely modern touch.

An isolated village literally built into the crevices and rock formations of a mountain.

This massive mural by famed pop-artist Keith Haring was hidden for almost 30 years until its 2018 rediscovery.

Three connected pink triangles memorialize persecuted gays and lesbians throughout history.

An ancient passage filled with stalls selling used books, once frequented by Vincent Van Gogh.

Dummies recreate radiological discoveries from history.

One of the deepest indoor swimming pools in the world.