The Shadow of the Torturer - Gene Wolfe
I return to this often, it's one of the few genre fictions that always rewards another visit.
Wolfe is up to many games here, cloaked in his version of the unreliable narrator, one in an unfamiliar exotic world where the rules are unknown.
There's plenty of action, and gore and political intrigue and fantastical events to satisfy, but the real meat is in-between, in some of the monologues, the dream-recollections, and the descriptive passages.
There's a Lovecraftian tale-within-a-tale that seems to be mining it's horror from explaining quantum mechanics and superpositions. A long dead mentor in a dream drills Severian on the basics of political philosophy, and much to our horror comes Severian's answers. Most disturbing of all is Severian's use of his guild's craft; torture and execution, as a glib metaphor for writing in general!

Deadly sentient plants used as dueling weapons. An ancient named sword. Creatures and monster of all kinds. Rooms built of illusion, whose use has been forgotten. Secret cults, stolen treasures. All here. But wrapped up by an omniscient narrator keeping secrets, or lying, to the reader. A dying future world with the barest of connections to our own. A lexicon of latin, greek, and nonsense to interpret and be memorized two or three times a paragraph. Poetry, improvised sideshow plays, lost histories, alien etymology.

Just finished it again, but I know I'll be back.