The clearest example I've ever found of a work that is both SF and fantasy.
Kilda is recounting the strange story that leads to her being about fifty years younger than she ought to be, given her birth and the year. She was raised in a creche, and the official assignments did not get her a place out of it until she was nearly aged out. Her mentor suggests an unofficial route, and she ends up taking service, and charge of two children Bartare and Oomart, as their mother and they ship out to the planet where he's working. Bartare is rather peculiar in behavior and intimidates Oomart -- Kilda hears things about She. Arriving on planet, they find that Bartare knows beforehand that their father died in an accident. The mother collapses, and Kilda continues to supervise the children. Bartare does many strange things, including one that seems to make everyone sleep as if drugged -- Kilda not having been in her room when she finished it.
But when they visit a sight on the planet, Bartare takes Oomart with her and goes off. Kilda follows and finds her performing another rite. Stumbling on this one means that she is caught up in it, and lands in another world. Oomart is nearby, but he sees landscape where she sees geometric shapes, until she drinks from a stream.
Where this ends up involves a strange, shaggy creature that dogs their steps, pieces of choc (a kind of sweet, if you can't guess from the name), extorting a promise by names and making specifications about what the promise entails, a maze that traps her, white flowers, a horn and a hunt, toes that start to try to take root in the earth, feet that turn to hooves, a distaste for food from their own world, and a wound that needs bandaging.