The action shifts to Balbec, a peaceful seaside town where Marcel comes to recuperate from his asthma. His grandmother and Francoise (who used to be his Aunt Leonie’s maid) accompany him. Most of the characters up until this point disappear, and for the first time, there is the sense of a real break. Given how tied “Madame Swann at Home” is to what went before it, as well as the sense of closure and expansion it provides over the entirety of Swann’s Way, the real division in the first two books lies here, not at the end of Swann’s Way.
The tone is considerably breezier and less intense, for which I’m grateful. Balbec is more sparsely populated than Paris or Combray, and Marcel himself begins to become a more active participant in what goes on around him. Unlike his affair with Gilberte, which seemed almost hermetically isolated from the larger community, Marcel himself has more prominence in the sparser landscape. He quietly matures in this section, primarily through his interactions with, first, his friendship with two boys, Saint-Loup and Bloch, and second, his involvement with the titular group of young women. He also, crucially, makes the acquaintance of the painter Elstir, who functions as a counterweight to the writer Bergotte, who dominated “Madame Swann at Home” but does not appear here.
I did feel a tone of liberation in this part, as though, free of the comings and goings of all the socialites in Paris, Proust can get down to Marcel’s individual development without detailing the constant movements of the society around him. Tied mostly to a hotel full of elderly shut-ins, there’s a sense of expansiveness and linearity. Even cheeriness, as evidenced in passages like this, which shows a sunny facility that hasn’t been dominant since Combray:

I felt on seeing her [a tall girl] that desire to live which is reborn in us whenever we become conscious anew of beauty and of happiness. We invariably forget that these are individual qualities, and, mentally substituting for them a conventional type at which we arrive by striking a sort of mean among the different faces that have taken our fancy, among the pleasures we have known, we are left with mere abstract images which are lifeless and insipid because they lack precisely that element of novelty, different from anything we have known, that element which is peculiar to beauty and to happiness. And we deliver on life a pessimistic judgment which we suppose to be accurate, for we believed that we were taking happiness and beauty into account, whereas in fact we left them out and replaced them by syntheses in which there is not a single atom of either. (705)

Maybe not completely sunny, but at least a yearning for it that is fulfilled later on. (There are hidden allusions: this passage rephrases an observation made about the novelty of Bergotte’s speech, on pages 592-593.)
The more abstract philosophizing recedes, but Proust still hammers some of his earlier themes, though he mostly doesn’t elaborate on them until the last hundred pages or so of “Place-Names: The Place.” In short: the role of our own images of people and things, the evolution and mutation of these things and images over time, and the uncertainty of the present moment. Above all of these, the refuge in the aesthetic and the imagined, rather than the reasoned and felt.