This question has been asked before, so you might find more information in the enotes links to Night. The author, Elie Wiesel, lived this story, so the images are burned into his mind. He is trying to convey to the reader the horror of being in the concentration camp by using images of people dying, fire, and his fight to save his father. The setting is primarily in the concentration camp because that is where Elie and his family were sent after they were rounded up by the Nazis. Their camp is a killing camp where people coming off the trains were often sent straight to the gas chambers and then the ovens to get rid of the bodies which is what happened to Elie's mother. The book has a grim setting and grim images because Auschwitz was a grim, horrific place.