In a flashback sequence that opens the film, Anna and Elsa’s mother Iduna (voiced by Evan Rachel Wood) sings a lullaby her mother used to sing to her when she was little, about a special river called Ahtohallan that was said to hold all the answers about the past and what they are a part of.

It foreshadows Elsa’s journey to Ahtohallan and is important later on in the movie as it guides Elsa’s journey. She also sings the song with Honey Maron after discovering she is Northuldra.