A male character is called "Hild", which is feminine name which is still common enough in Scandinavia. To Scandinavians ancient and contemporary, it would be like calling a girl "Chuck".
After being shipwrecked in the dead of winter, the remaining Vikings seem as dry as a bone. Not a shiver, not a sniffle, not an attempt to get dry. Their clothes should have been as stiff as boards. Absolutely ludicrous but in keeping with an appalling production overall.
There where no castles in 7th century Scandinavia. The major fortifications of that period where "ring forts".
Crossbows where not introduced in Scandinavia until the middle ages.