Peek through a transparent pyramid and drink in the mountain made of books.

This unattributed sculpture in Amsterdam is hiding in plain sight.

Inspired by "The Starry Night" this Dutch bike path turns into a glowing work of art each night.

This impressive collection of rare books on ancient mysticism inspired author Dan Brown.

A Portuguese Jewish cemetery filled with stunning grave monuments that date back to 1614.

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

A floating cat sanctuary on an Amsterdam canal.

Cat art as far as the eye can see.

These gigantic skeletons tower over visitors and provide insight into the creatures that once ruled over Ireland.

This courtly monument celebrates an influential comedian who turned taking the piss out of the powers-that-be into an art.

This is the largest cemetery in Ireland and the first cemetery museum in the world.

Though they've since been renamed, these two streets hint at Dublin's darker days.

More than 5,000 artifacts donated by the people of the city, plus a room entirely devoted to the band U2.

The mummified heart of a saint lives on in this church—after a brief hiatus when it was stolen.

This permanent collection of preserved bodies taken from Irish bogs is one of the leading authorities on such morbid mummies.

An 80-year-old plane tree is devouring an iron bench at Ireland's oldest law school.

The enchanting archway is the only surviving portal into Dublin's lost medieval wall.

A museum that cashes in on its infamous little people while teaching you a thing or two about the Irish fey.

The gorgeous library at Trinity College is home to remarkable treasures of Irish identity.

Six beautiful wooden giants are hidden around Copenhagen.

Hans Christian Andersen for the postmodern world.

Pre-Nazi swastikas adorn the sculpted pachyderms flanking this brewhouse portal.

This sublime architectural marvel is a rare example of an expressionist church.

A 19th-century subterranean reservoir repurposed as a contemporary art cave.