Final answer:
Elie Wiesel's statement 'Our eyes were open, but too late' refers to the moment of realization prisoners had upon arriving at Auschwitz, where they were to face horrifying fates.
Step-by-step explanation:
When Elie Wiesel said "Our eyes were open, but too late," he was referring to the realization of the horrors upon arriving at the concentration and extermination camp of Auschwitz (also known as Auschwitz II or Birkenau). Auschwitz, in western Poland, was the largest of the death camps and was notorious for its gas chambers where the majority of arrivals, particularly Jewish deportees, were immediately sent to their deaths. This statement reflects the delayed understanding of the prisoners about the true purpose of their transport to the camp and the tragic fate that awaited them.