Assess the importance of setting in Heart of Darkness

The setting is the basis of every story or novel, the basis of every prose work. Heart of Darkness is by no means an exception. Joseph Conrad's nouvelle or rather said mysterious work is not being easily understood let alone assessed. But each reader of Heart of Darkness should try to solve the mystery the author has opened.
The setting reveals itself to be a mystery within the mystery. What is really the setting of Conrad's nouvelle? And is it at all important to the work as a whole? Is it the usual setting of an adventure story that was popular at the time, is it a place of darkness, t…