The China Garden by Liz Berry is probably just an Honorable Mention as far as specific GU plot points, but I can’t overlook a story that begins by referring to the myth of Persephone’s descent, and includes an actual descent underground at the climax.
Clare has just finished her exams and is preparing for university when her mother announces she will be taking a job at an old estate in the English countryside called Ravensmere. Clare was planning to stay in London, but feels inexplicably drawn to accompany her mother. Once at Ravensmere, she has an instant connection to the place, and learns that in fact, her mother grew up in the area (unbeknownst to her). But Ravensmere is under threat now from a greedy, scheming land agent (the only person who really approximates an adversary) who wants to destroy it for profit – and with it, the mysterious “Benison” (blessing) that has been protected for centuries.
In just a few intense weeks, Clare uncovers the estate’s hidden history, finds a secret and magical garden, meets and falls for a young man from the neighboring farm, discovers her own latent psychic abilities, and begins to understand that she is next in a long line of guardians of this land. She treads a sacred maze and has visions that are leading her to a powerful secret, but she resists this calling, wanting to still have a normal life.
Eventually the ailing estate owner kicks out the evil land agent (one of the reasons this isn’t really GU, since Clare never confronts him), but has a stroke before he can tell Clare and Mark how to save the Benison. They must embark on a dangerous journey underground to find their life’s purpose and the land’s strength.