A boulder in the Churchyard of Down Cathedral marks the legendary burial place of "The Apostle of Ireland."

A relic of Victorian grandeur hides beneath a busy South London road.

A 400-year-old mummified arm dangles from the ceiling of St. James the Greater, serving as a warning to thieves.

Two stunning 17th-century libraries and a cabinet of curiosities.

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

A Jenga-style cylindrical tower of books that appears to go on forever.

This doorless 20th-century elevator doesn't stop or slow down.

Synagogue built from the stones of Solomon's temple contains the golem of Prague.

A mocking tribute to the past and modern leadership of Prague.

Dedicated to the man who saved hundreds of children from Nazi-occupied Czechoslovakia.

A saintly relic hidden in a Prague church basement.

A giant interactive periodic table with real samples of the elements.

Walk through Czech history in Prague's largest graveyard.

This artificial cave looks like something out of a fairytale.

A church of bones, decorated with 40,000 human skeletons.

The sanctuary holds what was once believed to be the saint's incorruptible tongue.

Mysterious painted skulls in Moravia.

Europe's second largest ossuary wasn't discovered until 2001.

Mummified monks and the accidentally interred, in a 17th-century crypt.

Heralded as one of the prettiest castles in all of Czechia.

The mystery of the Putim Ossuary involves a tricorn hat.

Thirty creepy ghosts now inhabit this decaying 14th-century church.

These 17th-century mummies are no longer naturally preserved, but remain on display today.

An overlooked collection of over 350,000 artistic works created by psychiatric patients using art therapy.