Final answer:
The Wanderer Above the Sea of Fog best captures the theme of time and human existence's limitations within it, emphasizing the impermanence of the individual against the immensity of the landscape.
Step-by-step explanation:
The painting that expresses the external theme of time and the limitation of our existence with the boundary of time is The Wanderer Above the Sea of Fog. This artwork depicts a solitary figure overlooking a vast landscape shrouded in fog.
The artwork captures the grandeur of nature while also emphasizing the transience of human existence as the figure seems small and ephemeral within the vastness of the setting.
The use of spatial relationships, perspective, and atmospheric perspective in the painting also contribute to a sense of depth, movement, and the passage of time.