About 1/3 of the way into vol. 2. Toru realizes that his wife has been having an affair when she doesn't come home one night. Her brother tells him it's because Toru is such a total waste of space -- he quit his job, has never really done anything with himself, and so on. Toru gets defensive, but admits to himself that it's true. So, to think things over, he goes down into a well to think things over.
This is one of the famous scenes from the novel, in the bit of reading I did about it before starting to read the book. If nothing else, it's very emblematic of Murakami's style; rationally, there's no reason why Toru should go into the well. In fact (as it turns out) it's a very stupid thing to do when he ends up stuck there. But in the context of the novel, it feels like an understandable thing to do.
And we finally start to learn something about the relationship between Kumiko and Toru, as Toru has flashbacks to their getting together, her getting an abortion, and so on. In this whole part of the book, Toru is finally less passive -- both in the present (yelling at his brother-in-law), and in the past (pursuing Kumiko, his reaction to the abortion). We also learn about the darkness that even then was in Kumiko's character.
Overall, vol. 2 looks to be a lot more intense than vol. 1.