And it was challenging because ...? Did it change your life or some other reason?
At a guess, I'd imagine many people would find the complete book challenging because of the unexpected material and viewpoints that can be found in sections of the Old Testament, like: https://www.biblegateway.com/passage/?search=Judges+19:22-30
On this topic, you may want to check out How to Read the Bible: A Guide to Scripture, Then and Now by James Kugel. It provides a historical overview of how the implicit and explicit interpretations of the old testament narratives have changed with respect to scholarship. Great read.
One can read the Bible on various different levels: as a historical document, a document specifically for you, and so on.
It has many surprises (like the example you gave). Heck, if the Old Testament was made into a movie, it'd be R rated.
My current favorite scripture is the origin of the pet. It's in Genesis 2:18-19. Adam was lonely in the Garden of Eden, so God provided Adam with animals for companionship. Adam gave a name to every one of his animal friends.
It's an endlessly fascinating book. I have many versions of it for study, but I prefer the King James.
It's literally the only book I've ever found unreadable (sequentially.) I tried really, really hard for weeks, and not just once. Multiple times over the course of different years.
man, forget it. It's easier to read a kernel dump.
At a guess, I'd imagine many people would find the complete book challenging because of the unexpected material and viewpoints that can be found in sections of the Old Testament, like: https://www.biblegateway.com/passage/?search=Judges+19:22-30