Charnel house at the foot of Mount Sinai.

An ancient ossuary in Rouen.

5,000 skulls in memorial to those killed by the Khmer Rouge.

Artfully arranged bones of 5,800 Austrians.

The personal charnel house of Anton Bruckner.

Skeletons dressed in extravagant 18th century royal costumes cavort in the aisles of this German basilica.

Thousands of well-dressed mummies below a monastery.

Mysterious painted skulls in Moravia.

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

The mortal remains of an estimated 70,000 people lie in the basement of a monastery in Lima, Peru.

The remains of 40,000 humans, meticulously stacked in a tiny churchyard shed.

Skulls from the plague of 1656 and World War II bombings are united by a cult dedicated to caring for the ancient dead.

This Peruvian bone silo lined with hanging human skeletons and hundreds of skulls is topped with a remarkable Michelangelo replica.

One of the largest ossuaries in Spain is packed from floor to ceiling with bones.

This German bone house contains the remains of some 20,000 souls.

A house of bones — but nobody is quite sure to whom they belong.

The walls and ceiling of this Polish church are decorated with thousands of skulls, with another 21,000 skeletons just below.

In 1830, cemetery workers in Cham unearthed a chamber housing thousands of skeletal remains from the 13th century, which can still be viewed today.

The vast, legendary catacombs hold secrets much stranger than stacked bones.

A church filled with the bones of hundreds of virgins martyrs—or so they say.

This landmark church concealed a crypt packed with bones that was discovered thanks to the London Blitz.

Underneath this small church are 15,000 bones, arranged by an obsessive academic.

A 1,000-year-old church holds the bones of the Christian martyrs who died hiding inside it.

The crypts of Capuchin friars decorated with the bones of over 4,000 friars, including an entire "crypt of pelvises."