Our family's favourite movie studio is Studio Ghibli. Ghibli's first animated feature film was Castle in the Sky (also known as Laputa: Castle in the Sky in some regions). It centres on Sheeta, a young girl who is descended from the royal line of Laputa, an island that floats in the sky. Laputa floats due to the power of a giant crystal of volucite (also known as aetherium in some versions). Volucite also enabled the Laputans to develop highly advanced technology and weapons, but at the time of the film, Laputa itself and its technology are largely mythical, having been abandoned and lost for many generations. Sheeta teams up with Pazu, an orphan from a mining town. His deceased father once took a photograph that included a glimpse of Laputa in the clouds, but it was disbelieved as a fake and Pazu is determined to vindicate him.
I would recommend people of any age to watch the beautifully animated movie, as I cannot do it justice in a few sentences. I will just add a few more notes below that were floating around my mind as I put this together.