This still-celebrated home was a radical architectural experiment in 3D De Stijl.

The Bauhaus-style former industrial complex is considered the world's most beautiful coal mine.

An expansive complex of subterranean tunnels is all that remains of one of Europe's most formidable medieval fortresses.

Around 100,000 bodies are buried below the medieval headstones, many of which mark graves with multiple bodies stacked up to 12 deep.

Macabre astrological automaton clock dating to the late 1400s.

Some of the greatest minds in the history of Hungarian art and science converged in this café.

A two-way chairlift system between Zugliget and the highest point in the city.

Budapest's Communist-era statues, banished to the suburbs.

A museum in the childhood house of a medical pioneer.

Once the home of a hermetic monk, this cave now houses a small church.

Built in 1870 at the bridge that connected Buda and Pest, this spectacular incline railway was almost lost forever during World War II.

A 19th-century artistocrat's mansion, turned into a library, hidden in a modern library.

The attic of a four-century-old canal house hides a clandestine church.

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

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

A unique collection of gilded age mechanical pianos.

The world's oldest Jewish library was founded by Sephardic Jews in 17th century Amsterdam.

A public urinal so pretty, it was declared a national monument.

This city square is home to Amsterdam's oldest church and a statue honoring Dutch sex workers.

A curious collection dedicated to human and animal anatomy and pathology.

Cat art as far as the eye can see.

This Corsican Neolithic site is full of pre-Roman megalithic structures that may or may not be penises.

Napoleon's childhood home is now open for people to explore the beginnings of France's short general.

One of the best collections of wax anatomical models in the world.