Suggest me a book that’ll prepare to write about existentialism, the pursuit of everlasting life, and the futility/acceptance of it all.

How’s it going everyone. I’ve recently been inspired to write a fiction book that tackles these topics, but I’d like to read more for further inspiration. Fiction and non-fiction work, but preferably fiction if only to also better learn how to write such a novel. Thanks, I’m excited to see the suggestions.

P.S. I was inspired mainly by the film, “The Man from Earth” and the novel, “The Picture of Dorian Grey”