Children Who Chase Lost Voices (2011 movie) by Makoto Shinkai, also known as Journey to Agartha.
Agartha is a world under the earth, a place of great beauty and also unimaginable dangers. It has a reputation as a place in which the dead can be brought to life. The young heroine, Asuna, sees a monster that has come up from below and is rescued by a boy, Shun, who has also come from Agartha. Asuna’s new schoolteacher, Mr Morisaki, turns out to know a lot about Agartha legends, and his beloved wife died some years ago. Asuna has also lost her father.
Asuna is dragged into Morisaki’s quest and enters Agartha, where she has a series of frightening adventures.
This movie is pretty good and has a somewhat darker tone than a typical Studio Ghibli movie. The animation is perhaps not as slick as a Studio Ghibli product and the resolution a shade muted.