The glacier Elsa visits at the end of Disney’s Frozen II is called Ahtohallan.
Ahtohallan is an ancient, magical river of memory described in the lullaby “All Is Found.” Elsa travels across the Dark Sea to reach it after learning that the source of the mysterious voice is connected to the glacier. Inside Ahtohallan, she discovers memories preserved in ice and learns more about her family’s history and the past conflict between Arendelle and the Northuldra.
The glacier functions as both a location and a source of knowledge. Elsa’s journey there reveals the truth about the dam built by King Runeard and helps her understand the origin of her powers. She also learns that Queen Iduna was Northuldra and that she saved Agnarr during the forest conflict.
Ahtohallan is often mistakenly called the Dark Sea, but the two are different. The Dark Sea is the dangerous body of water Elsa crosses; Ahtohallan is the glacier beyond it.