The answer is the afterlife.
In Shakespeare's play "Hamlet," the phrase "undiscover'd country" appears in the famous "To be, or not to be" soliloquy in Act 3, Scene 1. Hamlet uses this metaphor to refer to the afterlife, a place that is unknown and unexplored by the living. He is contemplating the nature of existence and the fear of the unknown that makes people endure the hardships of life rather than risk the uncertainties of death.
While Denmark is the setting of the play and a significant element in Hamlet's life, it is not what he refers to as the "undiscover'd country." The context of the soliloquy is more philosophical and existential, focusing on life and death rather than a physical location.
Foreign lands could be considered unknown to Hamlet, but in the context of the soliloquy, he is not speaking about geographical exploration. The "undiscover'd country" is a metaphor for the afterlife, not a literal place on Earth.
Hamlet's mind is indeed complex and filled with introspection, but the "undiscover'd country" specifically refers to the afterlife. The soliloquy deals with the fear of what comes after death, which is a central theme in Hamlet's contemplation.