These are the skulls of some 40,000 plague victims used to build a small chapel in a town just outside of Prague.
Though it might sound pretty grim and distasteful it didn't actually feel like that - macabre, certainly, but more unique than anything else.
Taken at Sedlec Ossuary, Kutna Hora.
Ossuary - 92/365 by
cedarsphoto, on Flickr