Note that as of now, this place is not given an actual location anywhere within the game world. It can be assumed that it exists somewhere relatively close to one of the major ruins due to its nature.
Sometime after the nuclear war, the government or rather what was left of some government tried to bury their dead outside the city. An old quarry was chosen as a site for a mass grave. No one today knows how many corpses were buried there, but considering the site consists of four hillocks, the best guess is “a lot of them”. The site was covered with earth and stone, and then forgotten once whatever government was responsible for the work stopped existing.
Now, the site is a place of dread for the inhabitants of nearby villages and farmsteads. The mounds are covered with stunted trees and bushes, and the flat terrain nearby is riddled by the hulks of pre-destruction vehicles and heavy machinery used for the burials. A large quantity of cut stones is spread around the site, probably left over from when the mounds were covered.
While the people nearby mostly ignore the existence of the Barrow-mounds, they still live in their shadow. Once the sun sets, people stay indoors. If someone knocks on the door then, they don’t open the door. Something is out there.
There are stories of shepherds and goat herders disappearing into the Barrow-mounds. Travellers on a nearby road might tell seeing some odd movement on the Barrows at dusk, which may spoil a fun evening if this is told at a local inn or bar. The locals really don’t want to know what’s happening there.
If pressed, someone might whisper the word “draugr”. If asked what this means, the locals might say “the hills eat people”. Because that’s what the draugr do. They are the restless hungry dead. The dead envy the living, is what people say about them. Maybe they’re right.
The draugr are partially incorporeal and often appear as emaciated human forms, characteristically with no eyes or lips. Not all of them appear emaciated though: some reports say they are bloated human forms with thick long-nailed fingers. They’re clad in rags and tatters, and sometimes appear in small groups and sometime alone. There’s no clear pattern to their behavior: sometimes a traveller might spot a draugr watching him passing and not taking any action. Sometime they seem to wander around farmsteads and houses, looking for a way in. You might want to keep your curtains drawn at night. There are no known survivors of a draugr attack, no witnesses to such an attack and never has anyone found a trace of their victims, apart from a dropped bag or a shoe. People just vanish.
As to their origin: no one knows why the draugr appear around gravesites. It doesn’t happen everywhere and it virtually never happens in more settled areas. The Barrow-mounds is the only place where the situation persists, elsewhere draugr might appear for a short while to then disappear.