Heart of Darkness by Joseph Conrad

'The mind of man is capable of anything - because everything is in it, all the past as well as all the future. What was there after all? Joy, fear, sorrow, devotion, rage - who can tell? - but truth - truth stripped of its cloak of time. Let the fool gape and shudder - the man knows, and can look on without a wink'
 
Marlow, a seaman, tells of a journey up the Congo.

His goal is the troubled European and ivory trader Kurtz. Worshipped and feared by invaders as well as natives, Kurtz has become a godlike figure, his presence pervading the jungle like a thick, obscuring mist. As his boat labours further upstream, closer and closer to Kurtz's extraordinary and terrible domain, so Marlow finds his faith in himself and civilization crumbling.