The Gothic church standing in Sedlec near the quaint Czech Republic city of Kutná Hora looks pretty ordinary from the outside, but head into the basement to discover something chilling: Bones of thousands of humans were bleached then ornately carved, and now artfully cover everything in sight.

As the story goes, a local abbot made a pilgrimage in the 13th century to Jerusalem and brought back some sacred soil to spread across the church cemetery. Word got out, making the Sedlec cemetery one of the region’s most popular places to be buried.

When the plague ravaged Europe in the 14th century, nearly 30,000 victims were added to the plots. The Crusades then brought 10,000 more casualties to rest in this particular cemetery, not to mention other burials followed over time.

When the community started to construct the Gothic church in the 15th century, many bones were moved and stacked in pyramids in the ossuary beneath the new building. Everything was left undisturbed until 1870, when the church hired a local woodcarver, Francis Rint, to create something beautiful from the staggering piles of bones.