What area in the bookshop is Henry's family most proud of in the novel, Words in Deep Blue?

The Letter Library is a small part of Henry’s family’s bookshop, but functions as the heart of the shop. It contains books that are not meant to be sold, but rather act as parts of a small library for people to browse when they are in the store. They allow readers to liberally mark up the books, and write to other readers of the same book. In fact, this is the pride of Henry’s family, and they all feel emotionally attached to it. Readers often go to it specifically to write to the members of Henry’s family, but also to other strangers. The regulars, who may not always speak to each other in person, still communicate through the books when they feel lonely or seek understanding.