Reading Here Be Dragons: Exploring Fantasy Maps and Settings by Stefan Ekman, I came across the work of Farah Mendlesohn. In her book Rhetorics of Fantasy, Mendlesohn suggests all fantasy novels can be placed in one of four categories, based on how the fantastic is introduced into the story. As Ekman describes them:
“The portal-quest fantasy introduces the point-of-view character into a fantasy world, either from a version of our own world (through, for instance, a wardrobe) or from a place in the fantasy world that, like the reader’s world, is ‘small, safe and understood’ (such as the noneventful, comprehensible Shire). The story is told from this point of origin, and the reader learns about the alien world along with the main character(s). In immersive fantasy, the characters, unlike the reader, are at home in the strange world, and the world is described as if totally familiar; the reader has to puzzle out how it works from the clues that are given. Intrusive fantasy is set in a world (often our own) into which the fantastic intrudes, causing chaos and confusion. Neither protagonist nor reader is familiar with the fantastic intrusion, and the story is a process of coming to terms with it. The ghost story is a typical intrusion fantasy. In the final category, liminal fantasy, the reader’s expectations are used to create worlds where the commonplace comes across as strange and wonderful, and the alien is portrayed with an everyday triteness bordering on the blasé. These fantasies are stories in which stylistic manipulation is central to the experience of the fantastic.”
Girls Underground stories are almost all portal-quest fantasies. A crucial element of the archetype is the girl leaving behind her normal life for an adventure in a strange new land. Her volition in taking that first step across the threshold is key (and results in a quest with one of a limited set of common goals, such as rescue of a loved one). However, a smaller number of GU stories instead fit the intrusive fantasy category, where the otherness bleeds into her normal life and changes its course. To me, though, these are usually less effective examples.