Valley Arnardalur is located 25 km south of farm Modrudalur a Fjollum. Bordering it to the east is a sand and gravel ridge called Dyngjuhals and to the west are the Arnardalur Mountains. The valley floor is a somewhat vegetated, flat plain through which River Arnardalsa runs. It collects some spring water from Dyngja and River Thrihyrningsa. Just above the confluence with Glacial River Jokulsa a Fjollum, a waterfall decorates River Arnardalsa. Traces of human inhabitancy of the valley were discovered at Dyngja. Heaps of bones of horses, sheep, whooper swans and geese along with net weights made of sheep bones and charcoal, probably from a garbage heap, were among the things unearthened there.
No written sources reveal the inhabitancy of the valley, but a legend tells us about the farmer at Bru in the Jokuldalur Valley, who fled with his people into the interior during the second plague in the late 15th century. According to this legend, he spent one year in Dyngja and two years at Netsel on Lake Anavatn before returning to Bru. A road to the south from farm Modrudalur (100 km; 60 miles) ends at the northern edge of Glacier Vatnajokull, at the Kverkfjoll mountain massif.