Circe is set in ancient Greece, mainly in the mythical halls of Oceanos and Helios and on the mythical island of Aiaia. Miller did not invent any of these locations, but she does describe them in rich detail. Oceanos and Helios's halls are beautiful and opulent. For example, Helios builds his house out of shiny obsidian that reflects the brilliance of his rays. However, by comparison with the wild landscape of Aiaia, these halls are stifling. Not only are the obsidian walls dark when Helios is absent, but their flat, mirrored surfaces are also emblematic of the rigid social hierarchy that governs Circe's family. If she tries to push back against this hierarchy, all it does is stand tall and throw her words back at her like her reflection.
Aiaia is supposed to be a punishment. Helios sends Circe there to exile her from the family after she reveals that she is a witch. However, the lush landscape turns out to be both more freeing and more nurturing than Circe ever could have imagined. The plants and animals respond to her care and cultivation. She is able to make her own rules. The island does not keep her entirely safe from trauma, but it does give her the opportunity to heal. Eventually, it becomes a place where she can raise her son and make a new family that defies the hierarchical social order that still governs Oceanos and Helios's halls. Under that order, Circe and Penelope would almost certainly be rivals. Circe would have little respect for Penelope, a mortal. Telemachus and Telegonus would hate each other, and Circe and Penelope would hate each other's sons. Outside the immediate sphere of other gods' influence, on an island with a wilder ecosystem, they are all able to nurture healthy, healing relationships with one another. They build an unexpected community.
The interplay between the two main settings helps Miller make an important point about family dynamics and social systems. Many of these dynamics and systems are in place, like Helios's obsidian walls, because someone has chosen them and because they seem like they are protecting everyone. However, as Circe finds on Aiaia, more freedom, fulfillment, and safety might lie outside the walls.