Conrad's "Heart of Darkness" is a truly compelling study of European colonization and exploitation of Africa, and the evils it imbued in those who partook in those exploits.
"Heart of Darkness" is a frame story (or, a "story withing a story"). The frame is of a group of men on a boat travelling down the Thames at dusk (turning into night - paralleling the descent into the darkness of the internal story), listening to a seaman, Marlow, tell a story about his experience as captain of a riverboat in the Congo. Marlow is a seaman by nature, with no attachments to any home other than the sea. He pursues and opportunity to work on a riverboat in Central Africa. Upon arriving in the dense jungle, he begins to hear about a "remarkable" man/genius/ivory-prodigy named Kurtz who is stationed upstream from his own post. After a number of months spent fixing his tin-can of a riverboat (despite a desperate need for rivets! rivets!), he begins his descent into the "heart of darkness" - Kurtz's post down the river. His journey reveals the corruption, evil, and disjointedness of those living in the jungle.
The prose of this dark story of the corruption of human nature is beautiful. The journey is rife with symbolism and beautifully portentous imagery. There is a prevailing suspense from the beginning of Marlow's tale, culminating in a Poe-esque realization - "The horror! The Horror!"
Despite the negative criticism from Chinua Achebe (author of "Things Fall Apart") of the portrayal of the African natives as speechless and uncivilized "cannibals," the story is very poignant. It should be remarked that the novel is told from the perspective of a European writing the perspective of an Englishman traveling to the Congo, and the prevailing language of the period. That said, I did not find the portrayal of the natives to be dehumanizing, in fact Marlow makes the point of humanizing them, elevating his horror.
I strongly recommend "Heart of Darkness" to anyone - it is a very quick read, and can easily be finished within a day - and is well worth the small effort!