I didn't know this fairy tale - a Grimm (brothers) notwithstanding. It is charming.
|The Glass Mountain|
A peasant has seven sons and no daughter. Finally a daughter is born, but is sickly. The father sends his sons to fetch water for her, in the German version to be baptized, in the Greek version to take water from a healing spring. In their haste, they drop the jug in the well. When they do not return, their father thinks that they have gone off to play and curses them and so they turn into ravens.
When the sister is grown, she sets out in search of her brothers. She attempts to get help first from the sun, which is too hot, then the moon, which craves human flesh, and then the morning star. The star helps her by giving her a chicken bone (in the German) or a bat's foot (in the Greek) and tells her she will need it to save her brothers. She finds them on the Glass Mountain. In the Greek version, she opens it
When her brothers return, she hides. They turn back into human form and ask who has been at their food. The youngest brother finds the ring, and hopes it is their sister, in which case they are saved. She emerges, and they return home.