As part of our continuing series of Lovecraftian finds in un-Lovecraftian places, Somerset Maugham's novel follows a Gauguin-like artist who is compelled to leave his job in London and family, and make a long voyage to Tahiti to live in poverty and produce weird paintings which nobody recognises.
All normal enough, barring a few casualties along the way, but when the narrator stumbles on Strickland's final, crazed paintings, he seems to slip through into another world --
"...It was the work of a man who had delved into the hidden depths of nature and had discovered secrets. … There was something primeval there and terrible. It was not human. It brought to … mind vague recollections of black magic. It was beautiful and obscene..."
- given the setting, you would not need to tweak it much to get a CoC scenario in which the driving force is not Art but something darker and more malevolent towards humanity.