Yet another book mentioned in Jane Austen's Northanger Abby, and yes, it's an actual book. It's a Gothic novel written by Matthew Lewis, and not too bad of a novel. It was published in 1796, and the author was about my age, too, at that point. (That's according to Wikipedia. If that's true, then he's lucky.)
Though I did say it wasn't too bad, it was the strangest I've ever read. So many twists and turns. . .it's crazy. Want me to basically say something? *Spoiler* Ambrosio has a lover. And he's a monk left on his own since he was a baby. However, he's the most strict and virtuous monk. Interested despite it's craziness? Give it a read. You won't get it out of your mind.