The Heart of Darkness was a famous novella by Joseph Conrad. It raises some disturbing questions about human nature and relationships. In it, Kurtz, originally intending to do good in the Congo, becomes cruel and monsterous in his treatment of the natives. He ultimately dies; and his final words are "The horror! The horror!" Years later, they made it into a movie entitled "Apocalypse Now," starring Marlon Brando and Martin Sheen.
Neither the book nor the movie are exactly light-hearted, if you know what I mean. And I suspect that the location of this heart of darkness in Conrad's book was internal in Kurtz, rather than geographical.
John Kennedy Toole wrote his outrageous comic novel A Confederacy of Dunces in the 1960's. In this work, the protagonist Ignatius O'Reilly described his going to Baton Rouge as going into the Heart of Darkness. Someone stole his hat with the ear flaps on that trip, which convinced him of the perils of travel to dangerous places. Actually, Baton Rouge is a pretty nice city with more to offer than Alexandria or Shreveport or Monroe.