The Shadow of the Torturer

This is runaway bonkers stuff. Set in a far distant future (millions of years) as the sun is starting its heat death process. The culture is medieval with swords, witches, guards that close the city gates at night, hand pulled wagons etc. The protagonist grows up in a strange monastic community that lives in a tower, but as the first book progresses there are hints that it's actually the remains of an ancient space ship standing on its end. Severian is being trained to be a torturer / executioner and the whole monastic thing is at odds with the hints of space ships etc.

The book is written as a memoir by the aged Severian and there are references of things to come that sometimes demand a bit of back tracking to sort out context etc.

Wolfe's terminology for weapons etc is often ancient and cryptic. You have been warned.

It's the first of four books (or five if we count the explanatory sequel) that are generally sold in pairs, Books 1 & 2, and then 3 & 4.