Early in Conrad’s 1903 novella, Marlow makes a comment “one of the dark places on earth”. About what place does he say this?

London

The story opens with an unnamed narrator describing five men, apparently colleagues, on a boat anchored on the River Thames
As dusk settles in and they await the turning of the tide. The narrator cites a passenger known as Charlie Marlow, the only one of the men who “still followed the sea.” Marlow makes a comment about London having been “one of the dark places on earth”; thus begins the story of Marlow and a job he took as captain of a steamship in Africa.

Heart of Darkness (1899) is a novella by Polish-British novelist Joseph Conrad, about a voyage up the Congo Riverinto the Congo Free State, in the heart of Africa, by the story’s narrator Marlow.^[1] Marlow tells his story to friends aboard a boat anchored on the River Thames, London, England. This setting provides the frame for Marlow’s story of his obsession with the ivory trader Kurtz, which enables Conrad to create a parallel between London and Africa as places of darkness

Discovery channel exploring the dark places