What metaphors are used in Invitation to a Beheading by Vladimir Nabokov?

Cincinnatus C. is a prisoner sentenced to death. His crime is not something he's done, but instead a condition of his being. Cincinnatus is introverted, focusing constantly on some internalized idea of the soul, heaven, and humanity. Everything surrounding Cincinnatus in the world seems false and illusory: only a metaphor of reality.