Under the Volcano
Author: Malcolm Lowry
One of the best novels ever written about alcoholism's destructive nature, Malcolm Lowry's Under the Volcano, inspired by his own struggles with the bottle, is an equal parts unsettling and riveting descent into Lucifer's playpen.
In this case, Hell takes the shape of Quauhnahuac, Mexico, where British consul Geoffrey Fermin spends his last day alive on what also happens to be the country's annual Day of the Dead. That said, Under the Volcano isn't a horror novel, at least not in the traditional sense. It's hard to label a man's losing battle against booze as anything but horrific, though.
Fun Fact: Lowry's original manuscript was nearly lost in a fire, in 1944, that engulfed his shack in British Columbia; thankfully, his wife grabbed the book-in-progress before it could go up in flames along with several other unfinished manuscripts.