Chapter 10, by far. It went on forever, was very repetitive, and the story "development" in it annoyed me. I didn't really care for any of the "dungeons" though; Orphan's Cradle was completely random and also repetitive. You could tell the writers had just given up when you're randomly teleported to fight a completely random boss and then magically teleported back to where you were. It was like a parody of random boss fights.

Compared to those two, Taejin's Tower wasn't too bad.