Fenja and Menja

Grottasöngr or the Song of Grótti is an Old Norse poem, sometimes counted among the poems of the Poetic Edda as it appears in manuscripts that are later than the Codex Regius. The tradition is also preserved in one of the manuscripts of Snorri Sturluson's Prose Edda along with some explanation of its context.

The myth has also survived independently as modified Scandinavian fairy tales, one of them called Why the Sea Is Salt, collected by Peter Christen Asbjørnsen and Jørgen Moe in their Norske Folkeeventyr. Moreover, Gróttasöngr had great social and political impact in Sweden during the 20th century as it was modernized in the form of Den nya Grottesången by Viktor Rydberg.

Though not originally included in the Codex Regius, Gróttasöngr is included in many later editions of the Poetic Edda.Gróttasöngr is the work song of two young slave girls bought in Sweden by the Danish King Frodi (cf. Fróði in the Prose Edda). The girls are brought to a magic grindstone to grind out wealth for the king and sing for his household.

The girls ask for rest from the grinding but are commanded to continue. Undaunted in their benevolence, the girls proceed to grind and sing, wishing wealth and happiness for the King. The King, however, is still not pleased and continues to order the girls to grind without interruption.

King Frodi is ignorant of their lineage and the girls reveal that they are descended from mountain giants. The girls recount their past deeds, including moving a flat-topped mountain and revealing that they had actually created the grinding stone they are now chained to. They tell him that they had advanced against an army in Sweden and fought "bearlike warriors", had "broken shields", supported troops, and overthrown one prince while supporting another. They recount that they had become well known warriors.

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Wikipedia