What is the significance of the title, The White Castle?

The white castle is significant because it represents an ideal, such as Hoja's Truth, Plato's Forms, or Kant's “Ding an sich” (thing in itself). It does not exist in real life, except as a pure concept. “It was at the top of a high hill, its towers streaming with flags were caught by the faint red glow of the setting sun, and it was white; purest white and beautiful” (143). The narrator writes that he knew “that our soldiers would never be able to reach the white towers of the castle” (143). Doppio (“double” in Italian) Castle, like Don Quixote's ideal, is unattainable.