The university library shaped like a giant piece of Swiss cheese.

The idyllic island where the philosopher Jean-Jacques Rousseau spent “the happiest time of his life.”

Artworks by loners, prisoners and the criminally insane.

Two geological phenomena in one precarious locale: a towering stone window, and a deep blue void.

This unique building in the main square stands out among the city's typically Baroque architecture.

This subterranean necropolis holds three floors of antler-dug grave caves.

Stone Age solar temple is aligned with the sun on each equinox and solstice.

Hidden beneath a beautiful overlook you’ll find the history of the city depicted in comic strip format next to a pay toilet.

Elaborately carved to showcase the glorious wealth that the age of exploration brought to the Portuguese empire.

The world's oldest bookshop still in operation.

Legacy of the earthquake that nearly wiped Lisbon off the face of the Earth.

This Industrial Age architectural and engineering gem helps visitors and residents alike traverse Lisbon, “The City of Seven Hills.”

A king's pet, a pope's gift, an artist's inspiration, and a tragic shipwreck.

London's last remaining public soapbox site has seen speeches from Karl Marx, Vladmir Lenin, and George Orwell.

Eighty million natural history specimens call this gargantuan museum home.

The popularity of Sherlock Holmes led to the creation of his fictional address, turning the orderly London street numbers askew.

The bunker where Hitler took his own life is hidden under this deliberately ordinary parking lot.

Thousands of coffin-like pillars make up this controversial Holocaust memorial.

The most visited, and possibly most controversial, museum in Germany.

An eclectic art form practiced by untrained masters is celebrated at this museum in the heart of Zagreb's old Upper Town.

Where the lovelorn find a home for their sentimental keepsakes.

One of the world's largest collections of pharmaceutical artifacts.

The bizarre visions of H.R. Giger, tucked away in a Swiss medieval city.

This lovely little bridge hidden in a Switzerland gorge is essentially a fairytale.