The Book of the New Sun, a sci-fi tetralogy by Gene Wolfe. Comprising The Shadow of the Torturer, The Claw of the Concilator, The Sword of the Lictor, and The Citadel of the Autarch. One of the most complicated and interesting works of sci-fi from the 20th century.
The Book of the New Sun is the Dark Souls of Books
Gene Wolfe and Dark Souls are both difficult and engrossing. In demanding rereading and replaying, they resist the passivity of consumer culture.