The Sedlec Ossuary (Czech: Kostnice v Sedlci) is a small Roman Catholic chapel, located beneath the Cemetery Church of All Saints (Czech: Hřbitovní kostel Všech Svatých) inSedlec, a suburb of Kutná Hora in the Czech Republic. The ossuary is estimated to contain the skeletons of between 40,000 and 70,000 people, whose bones have in many cases been artistically arranged to form decorations and furnishings for the chapel.
Wiki Page: http://en.wikipedia.org/wiki/Sedlec_Ossuary
This place is on my top 10 list of must see places before I die. It has been the source of a lot of rp inspiration, story inspiration, and more.