The oldest Holocaust survivor, Antoni Dobrowolski, who went to Auschwitz as punishment for teaching young poles has died at 108. The article quotes him as saying that Auschwitz was "worse than Dante's hell".
My initial reaction was that this is surely an overstatement. But a moment's reflection suggests that Dobrowolski is correct, at least as concerning hell itself (I won't comment on Dante's hell, since I am no Dante scholar). Hell is a place that upholds the dignity of its inmates by acknowledging their autonomous choice for evil, giving them justice and limiting their downward moral slide, while the concentration camps aimed at the destruction of autonomy and dignity. It is a terrifying thought that we humans can produce something worse than hell.
But at the same time, we have to remember that in a choice between hell and Auschwitz, we should choose against hell. So perhaps hell is worse? Or maybe we need to distinguish: in itself, in some sense, Auschwitz is worse, but hell also guarantees lack of union with God, while Auschwitz is compatible with union with God, just as the Cross was.