Howard Phillips Lovecraft (1890-1937) was the author of many short stories and the father of cosmicism. He wrote about a universe that is utterly meaningless and the cosmic horrors that live therein. He is considered the greatest writer of horror to live in the age after Poe and before Stephen King.
Tentacles? Forbidden knowledge? Esoteric cults? You must be reading an H. P. Lovecraft story.