“. . . I had stepped into the gloomy circle of some Inferno.” (52)

Conrad compares Marlow's situation to the hell described by Dante Alighieri in the first volume of his Divine Comedy. This is significant because it shows that Marlow really thought that his situation could get no worse and there was truly no getting out: he was going to be stuck in his own version of purgatory –the Congo - for the rest of time.

EDIT: It is not the Devine Comedy, but the Divine Comedy.

Source:

"Divine Comedy Summary." Divine Comedy Summary & Study Guide. E-notes. Web. 24 Aug. 2009. http://www.enotes.com/divina-commedia.