The Full Gufa trophy / achievement in God of War Ragnarok is unlocked once you free both Hafgufas in the realm of Alfheim. One of these is in The Barrens region, while the other is in The Forbidden Sands. Both regions will be plagued by a sandstorm until their respective Hafgufa is freed, so it’s necessary to do this in order to fully explore the regions. There’s a favor associated with the freeing of each Hafgufa, with Secret of the Sands for The Barrens region and Song of the Sands for The Forbidden Sands region.
Free the Hafgufas