What was the most difficult book you have ever read?

For me it was W.G. Sebald’s The Rings of Saturn. This book—about a German-English professor walking along the coast of East Anglia while talking about the philosophies of Thomas Browne, silkworm cultivation, old landmarks and coastal towns with illustrious pasts now since lost in irrelevancy, the life story of Joseph Conrad, and switching his perspective to those of the people he meets with whiplash suddenness—broke my Gen Z mind.

I’m curious to know which books made you feel more or less like this.