What is the importance of Auschwitz Two-Birkenau in the novel, The Tattooist of Auschwitz?

Birkenau is the camp within the Auschwitz network that the characters in the novel are sent to. It acts as both a concentration and extermination camp, and thousands of Jewish men and woman are tortured and killed here. The characters must fight to survive each day as they labor surrounded by electrified fences, under the watch of SS officers, and undergo inspection and experimentation by Doctor Mengele. The prisoners live in numbered blocks, work in numbered or nicknamed warehouses, and are sent to their deaths in numbered crematoriums. New deliveries of prisoners arrive at all times of day and night.