Ossuaries—chambers for storing human bones—are commonly described as places founded to house skeletal remains when cemeteries were overcrowded and burial space was scarce. But to focus solely on the functional would be selling these grim bone houses short.

Throughout ancient and medieval times and in the Catholic and Orthodox faiths, displaying and maintaining the bones of the deceased was a way to honor the dead. Thus today you’ll find ossuaries and churches spread across Europe, decorated with artfully arranged skulls and skeletons. While some ossuaries are more macabre, such as mass crypts dug for tens of thousands of plague victims or fallen soldiers, others are beautiful churches and chambers adorned with the bones of departed souls. Visiting the halls of the dead today is a fascinating reminder of our own mortality, one of the only certainties in life, and a way to ponder the eternal question of what happens after the soul leaves behind our mortal remains.