Čachtice Castle (Slovak pronunciation: [tʃaxtʲɪtse]; Slovak: Čachtický hrad, Hungarian: Csejte vára) is a castle ruin in Slovakia next to the village of Čachtice. It stands on a hill featuring rare plants, and has been declared a national nature reserve for this reason. The castle was a residence and later the prison of the Countess Elizabeth Báthory, who is alleged to have been the world's most prolific female serial killer.