A Canticle For Leibowitz touches on a similar theme.

I agree. I started with Anathem then went to A Canticle for Leibowitz. Together they were a fun read, I've put them both on my bookshelf.

I remember "reading" that as a kid, when I was too young to really understand the text, and thinking it was a horror story.

Is this the one where they find the toilet seat and think it's jewelry or something? If so, had the same experience. I was too young to understand it and thought it was something scary.

Yep, exactly! Tons of shadowy pictures of decayed skeletons lying in beds and bathtubs, and most of the humor is in the text.