Where It All Goes Down
Brooklyn
We can't think of any two more different settings than small town Ireland and big city Brooklyn. Given this, you can understand why Eilis is so affected by her travels between these drastically distinct locales.
The Concrete Jungle
Brooklyn is defined by its hustle-and-bustle. Although Eilis loves spending time on quiet, tree-lined residential blocks, our most enduring image of the neighborhood is the traffic on Fulton Street being so bad "that on the first morning she thought a fight had broken out" (2.20). Although Eilis is intimidated by these big city vibes at first, she eventually grows comfortable in the diverse, high energy world of BK.
Eilis' relationship with Mrs. Kehoe's boarding house is a bit more complicated. A small building filled with Irish girls and owned by an Irish landlord, this boardinghouse serves as a half-way point between Ireland and America, which has its benefits and its downsides. Regardless, Eilis finds herself most comfortable in her isolated basement room: she "loved putting her books at the table opposite the window when she came in at night and [...] spending an hour" quietly studying (3.156). Even when everything else is falling apart, this room is Eilis' sanctuary.
The Blarney Blues
Despite this, we don't fully appreciate how much Brooklyn changes Eilis until she returns to Ireland. There, her big city ways contrast sharply with the small town vibe of her hometown, where everyone knows everyone and gossip is a way of life. Eilis' childhood friend Nancy can see these changes as soon as Eilis arrives, observing that "everything about [Eilis] is different, not for those who know [her], but for people in the town" (4.183).
The Lacey family home is even weirder. It's like a bizarre trip back in time for Eilis: her mom "had left everything [...] exactly as it was" in Rose's bedroom following her death, "including all of Rose's clothes in the wardrobe" (4.1). Likewise, Eilis' own room has been stripped of all her belongings and is instead just a guest bedroom now. This, as it happens, is an eye-opening experience for Eilis. Although she loves her homeland, she now knows that the only place where she belongs is the big city.