Marlow’s journey up the river can be considered a quest because he seeks knowledge as well as tries to reach a geographic location. There are two key and interrelated aspects to his quest. The first part is to find Kurtz, which he has been commissioned to do because the ivory agent has apparently gone rogue. The other aspect, which is one reason he accepts the assignment, is to try to understand Africa. Marlow not only wants to travel in Western and Central Africa, but he wants to broaden his comprehension of how people live in an area that is different from “civilized” England.
In the course of this journey, Marlow does find Kurtz. His experiences while going up the river force him to confront his ignorance about Africa and to learn unexpected things, including the oppressive effects of European colonialism. Through his interactions with Kurtz, although they are brief, Marlow learns about how excessive power can affect all aspects of health, as the fatally ill man has apparently had a severe mental breakdown.
Since I had peeped over the edge myself, I understand better the meaning of his stare, that could not see the flame of the candle, but was wide enough to embrace the whole universe, piercing enough to penetrate all the hearts that beat in the darkness.
Both his interactions with Kurtz and the impressions from his voyage lead Marlow to deeper introspection, as he is compelled to wonder how he would behave in the same situation. Although Marlow did not seem particularly interested in gaining self-knowledge, he is forced to consider the heart of darkness that lurks within every human being.