B2/C1 reading level German Novels?

Bit of an odd question, I know, but I'm looking for recommendations on German literature that would make for a fun reading experience for a non-native speaker.

My German level is above a B2 but in less than a month I'll be starting my mandatory military service in Greece, which will last over 9 months and I don't want to lose any of the progress I've made in the last 2 years living in Germany and learning the language.

I've read a couple articles for ideas but I saw writers like Goethe and Hesse being named and I honestly just chuckled. As of writing this, I'm reading an English translation of Hesse's Siddhartha and some words just go right over my head. Considering the book's themes and exploration of spirituality, I know for a fact I wouldn't have a good time reading it in German. I'd assume the same thing applies to Goethe's Faust.

Also, if you could recommend a good self-learning B2-C1 grammar book that'd be great!

Novellas/Short Story books also welcome!

Any genres, strictly excluding Romance (unless there's a romantic sub-plot or whatever)