We are guided throughout Marlow’s journey by an nameless passenger listening to Marlow’s tale, as well as Marlow himself. As Marlow starts his journey and directs his way into the Congo, the cruelness of human nature and finally understanding, we begin observe an unforgettable journey into the depths of the darkest part of our human heart. In Heart of Darkness, there seems to include the Supernatural Aid, Call to Adventure, The Crossing of the First Threshold, and the Belly of the Whale in Marlow's journey in Africa. The Call of Adventure first appears as the snake of the Nile River with its tail "lost in the depths of the of the land." He claimed it "charmed him" (Conrad 5-6). In his journey, Africa was probably unexplored by the Europeans at this point in time that marks the beginning of his journey as he travels within the depths of Africa.
The Supernatural Aid surprisingly comes from Marlow's aunt that aided him in his journey by getting him a position on the riverboat. Have not known the place he was traveling to, Marlow becomes embedded into the center of the Earth and becomes a savage himself, leaving his own country behind. This is known as the Cross of the First Threshold because Marlow forgets his own world as he journeys on to Africa, not knowing the dangers of what's within.