The Tombs of Atuan by Ursula K. Le Guin, 1970.
A good work, intense, well-written and meaningful. Far from the quality of Lavinia or Le Guin's Hainish Cycle stuff, but quite rewarding, and a lot better than A Wizard of Earthsea. The story concerns a girl that becomes First Priestess, which mostly involves living underground and performing human sacrifices.
Very strong exploration of what magic would actually involve, making this a lot more than just flashy effects or convenient plot motivators. Rather, it's about naming, identity, perception, spirituality--all of which connect thematically to the larger journey of the book, particularly as Tenar is renamed and redefined for ritualistic ends. More than the slow build up to escape and travel, that's what the book is explicitly about: the function of religious questions in the invented world, and the tensions that ensue. Glorification and sacrifice, sanctioned and illicit beliefs, real gods and ritualistic forms. The book incorporates a lot of angles, and it works because Tenar is so ambivalent, believably uncertain about her rights in both authorizing murder and in leaving the environment. That she's able to have this range without being a weak or indecisive character speaks to Le Guin's high skill in both characterization and plot. And, the eventual escape from the titular Tombs of Atuan is awash in gorgeous description and themes, expressing very potently the emergence from a secluded mono-environment to the wider diversity of the planet.
Interestingly the work rarely feels claustrophobic, having enough intensity and range of description to come across as a complete environment. The main action is oddly closed in for Le Guin, though, as shown most prominently by there being only four real characters for most of the narrative. This is one of the areas where the work most benefits from being fantasy as opposed to SF--there's little need to offer an extensive worldbuilding (although the fact that this is part of a larger series also helps with that) so the description of hearing about and seeing the larger world can remain centered in the relevance to Tenar, in engaging with his past beliefs, overturning some, and connecting with basic influence of stories. This work isn't quite as meta as Lavinia in that regard, but it offers food for thought in that area as well.
Similar to and better than: Terry Pratchett's Pyramids
Similar to and worse than: Ursula K. Le Guin's Lavinia