I don't know exactly which church you mean. I know one, that of Santa María de Wamba, in Valladolid, which has an old ossuary full of human bones. Maybe you mean that. But bones in churches used to be common, not only because they all had their own small cemetery added, but also because some of the bones of the deceased were used in certain ceremonies, which are no longer in use today. Thank you very much for your comment and best regards.