not finding the key that opens the door, that's suppose to be in this cave, the one where you find the troll magic you need to destroy and the notes of the mother and her grotesque or deformed son, Grendel. has a marker for the key but no key to collect.
@jimmywon34 Can you confirm if you own the Season Pass for the game? As there is a known issue where the key icon will appear using Odin's sight, however the key is not visible and cannot be collected if you do not own the Season Pass to access the Legend of the Beowulf quest.
If you do own the Season Pass have you collected the letter from Eivor's room in the longhouse to start the quest?
Hello there @jimmywon34!
As shared by @SpirantCrayon22, the key will only appear as you progress through "The Legend of Beowulf" quests. If you're still unable to find the key whilst completing these quests, please don't hesitate to update us so we can investigate further.
Thanks! 
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