During Elsa and Anna's journey, they learned that their parents' ill-fated trip was one to Ahtohallan in an attempt to find answers about Elsa's powers. The Water Spirit who guarded the sea opposed Elsa when she tried to reach Ahtohallan. She was eventually able to tame the spirit and use it to take her to Ahtohallan.
Approaching, Elsa realized that the river was a glacier, a "river of ice". Elsa then entered and called to the voice while traversing through several tunnels and chambers, overcoming the obstacles she faced before coming into contact with a large, dark space. Once inside, the elemental symbols unveiled themselves in the form of large diamonds. After guiding them to the floor and standing in the center of them, the space became awash with images of the past.
Elsa was shown the source of the voice: her mother calling to the Wind Spirit while holding an unconscious Agnarr. From there, she learned that her powers were a gift from the magic of nature as a reward for Iduna's act of saving her enemy. By virtue of this, Elsa became the Fifth Spirit, a bridge between humans and nature.
Elsa saw memories of her grandfather, King Runeard, and found the truth about the past: the dam was not a gift of peace, but a trick to weaken the Northuldra. Elsa then went down further into Ahtohallan to discover the truth of what happened that day in the Enchanted Forest, seeing Runeard assassinating the unarmed Northuldra leader. Elsa slowly began to freeze; before doing so completely she was able to send out a message to Anna about what she had discovered.
After the dam was destroyed, and so the wrongs of the past righted, Elsa unfroze and the ice beneath her shattered, sending her falling into a large pool of water. Elsa was then able to ride back to Arendelle and save the kingdom.
Ahtohallan is a frozen magical river that knows everything about the past. This ability is based on one of the rules of the Frozen universe - water has memory.
Because it is made of ice, Elsa can use her powers to get into Ahtohallan and see the memories of the past hidden in it.
If one enters the deepest parts, one will be 'drowned' as the lullaby says - frozen into a solid ice statue, not unlike the memories brought to life by Elsa. Even Elsa, who is normally immune to freezing, becomes encased in solid ice.
- The filmmakers visited Icelandic glaciers for inspiration.
- According to Idunna in Dangerous Secrets, Ahtohallan is the "mother" of the other spirits.
- In Finnish folklore, 'Ahto' is the god of sea or generally waters and 'hallan' means 'frozen', so 'Ahtohallan' means 'god of frozen waters'.