The dungeon level in this book is called “The Tangle”, and the author manages to make his exposition just as confusing as the setting. I guarantee you that at some point you will just tune out whenever he starts discussing train station numbers, portals, train line colors, where the trains go and what they connect to, and the like. It’s impossible to follow. It really detracts from what would have been a good story had it been set differently, because you can’t understand why the characters are doing stuff. Why are they moving to station 24? Why does he need to use some particular portal type? The author gives you no help. It’s really surprising the book turned out this way because he did such a great job of world building and exposition in the prior two books. I’d say skip it, but since this is a series, you can’t. Slog through it, I guess. If book 4 has the same problem, I’m going to drop out.