Suggest Me a Book that is Challenging but Not Depressing

Looking for a Mild Flex here…

Open to Genre except no Horror & No Romance (Some romance Ok)

Edit to Add:
I like action- sexy reads. Sex & violence. So thrillers are good but I also want to be challenged & I don't want to be left feeling icky in any way.

(If it helps, I'm a witchy pagan weirdo)