Final answer:
Hamlet's statement 'Denmark's a prison' uses a metaphor to express his feeling of being trapped and surveilled at Elsinore, much like in a panopticon.
Step-by-step explanation:
When Hamlet refers to Denmark as a prison, he employs a metaphor, a figure of speech that implies a comparison between two unrelated things without using 'like' or 'as'. In this case, Hamlet is not suggesting that Denmark is literally a jail but rather that he feels as confined and oppressed as if he were in one. This statement reflects Hamlet's profound dissatisfaction with the state of affairs in Denmark and his feeling of being trapped by the circumstances surrounding his father's death and his mother's hasty remarriage.
The allusion to Elsinore incarceration or Elsinore prison emphasizes how the royal court, where Hamlet lives, represents a space where he is under constant surveillance and restriction, akin to the panopticon concept. This metaphor enhances the play's themes of confinement and the character's psychological turmoil.