Looking for a post-apocalypse that’s so far post that it’s turned back into a medieval type book.

Alright, this feels pretty niche. But I think my favourite part about The Dark Tower series was all the references to old, forgotten tech. Wolves of the Calla is a western in a post-apocalypse with a robot. It's pretty great! I'd really love books with advanced forgotten civilizations – the amount of answers or discovery [...]