Complex sentence: Denzinger is notable for having been a guard at five separate concentration camps across three countries, those being: the Auschwitz Concentration Camp and Plaszow concentration camps in Poland; the Mauthausen Concentration Camp in Austria; and the Sachsenhausen concentration camp and Buchenwald concentration camps in Germany.
Split into simpler sentences: Denzinger is notable for having been a guard at five separate concentration camps across three countries. Those camps were: the Auschwitz Concentration Camp and Plaszow concentration camps in Poland; the Mauthausen Concentration Camp in Austria; and the Sachsenhausen concentration camp and Buchenwald concentration camps in Germany.