Complex sentence: During World War II the manor became a Gestapo prison, through which more than 11,500 prisoners passed; the grounds contain a mass grave holding the majority of the 849 detainees murdered there.
Split into simpler sentences: During World War II the premises functioned as a Gestapo prison, through which more than 11,500 prisoners passed. Abutting the manor is a mass grave holding the majority of the 849 detainees murdered there.