If you are approaching from the north, you may already have seen Godafoss falls.
Sharing the same river but totally different in character, Aldeyjarfoss is a stunning 20m high waterfall situated at the northern end of the Sprengisandur mountain route, but accessible (with care) in summer to normal cars. Because the falls face north, the best time to photograph them is late in the day.
From the car park, where you'll also find toilets, a steep and gravelly footpath descends to the edge of the waterfall. Pause for the view of the rapids downriver of the waterfall, as they fan out across the river bed.
Aldeyjarfoss is unusual because of the surrounding cliffs of jointed columns, lined up like a church organ. The columns have been revealed by river erosion.
Originating from Vatnajokull, the river Skjalfandafljot flows alongside the western edge of the 5000 sq km Odadahraun lava expanse that takes up much of the uninhabited interior.
The vegetation is very sensitive in this area, so visitors are asked to stay on the path.