The ossuary in Sedlec, just outside Kutná Hora in the western Czech Republic houses the most amazing collection of art created with human bones as the raw material.
On the outside it's a fairly average church called the All Saints Cemetery Chapel that was built in the 14th century. The church is part of a Cistercian monastery that was founded in 1142. According to legend the monastery's graveyard had been sprinkled with some soil from the Holy Sepulchre that an abbot had brought with him from Jerusalem late in the 13th century. This led to a huge number of people from all over the region wanting to be buried in this more-than-hallowed ground, on top of the large number of "regular customers" that plague epidemics and a history full of battles brought its way. After about 30000 people were buried there space inevitably became a problem but removing the remains from the site was not an option. Starting in 1511, bones from old graves were stacked inside the chapel in pyramids.
In 1870, after the cemetery was turned over to real estate development, the monks came up with the solution to the bone problem and commissioned a woodcarver by the name of Frantisek Rint to do something with them. Rint used the bones to create an astonishing display of art by using the bones not just for decoration but also for practical items such as the chandelier (which is made of every bone in the human body) and the altar. His works include the coat of arms of the Schwarzenberg family, which owned the monastery at the time, large bells and chalices made of, you guessed it, bones. The artist signed his name on a wall... in bone. It's estimated that the bones of about 40000 individuals were used in the artwork.
Factual sources:
Several, mostly local guides.