Vallbyåsen, Uppland, Sweden. (2017) Close-captions useful..
Note: "Uppland ... is a historical province or landskap on the eastern coast of Sweden, just north of Stockholm, the capital." (Wikipedia) I'm not sure where this grave field is located exactly.
Broborg, the fort, is "a hillfort located around 10 km east of Knivsta [south-central Uppland]. It overlooks an ancient major waterway ... leading to the interior of Uppland, as well as a road. The location thus suggests that, in prehistoric times (and before too much elevation of the land), Broborg could have controlled access for trade as well as any military activities." Source: The Mystery Of The Vitrified Hillfort. (PDF)
Broborg was a vitrified fort, i.e., its stones were apparently cemented together by a kind of glass formed by subjecting stones to extreme heat. The article quoted above mentions that the vitrification process used at Broborg is being studied by modern scientists for its possible application in nuclear-waste disposal. The idea is to seal the waste inside a vitrified matrix to prevent it from escaping into the environment.
According to the description for the first video above, there is a legend about Grimsa, "a Viking queen who was burned alive in the fort," but I haven't been able to find any further information about her.
Video from 2013.