Photo from Wikipedia

Hafragilsfoss waterfall is one of the three best known waterfalls in Jökulsá á Fjöllum, along with Dettifoss and Selfoss waterfalls. The waterfall is about one and a half kilometer north of Dettifoss, and you can reach the waterfall both from east and west side of the river canyon. The waterfall is magnificent and extremely powerful about 27 meters high and about 90 meters wide.

Directions:

From Ring Road nr.1 take road nr 864 for about 25 km (30 minutes). The road is a gravel road and usually not passable during winter months.
It is also possible to access the waterfall from the East side, road nr. 862.

On the west side of Jökulsá river: Road number 862 usually open from May/June and until the beginning of October.
On the east side of Jökulsá river: Road number 864 a gravel road, no winter service on the road.