The approach we took (leaving from the Hrauneyjar Highland Centre) was by going west along route 26 for about 6km. There's a turnoff on the right hand side crossing the bridge over the Tungnaá then going onto black-sanded tracks. From here, the signs are a bit faint so you have to pay close attention.

At about 4km off route 26, we turned right, then continued on the black-sanded road following the signs the best we could finally reaching the falls after around 18km. The last several kilometres was what involved going over very deep mud ruts and seemed like we were driving on grass. It also seemed like the intention was to make this was one-way as rocks were set up to make it hard for you to go back the way you came. Along the way, you might notice other waterfalls like Gljúfurleitarfoss nearby (though they're difficult to photograph).

On the way back, we started to hit very scary boulder fields a little over 2km out. Once you get past that hairy stretch, the rest is fairly smooth going. Just be careful not to miss a right-hand turn about 2.5km past the boulder fields. We managed to miss it the first time and fortunately we figured out we went the wrong way (because the landscape and road obstacles didn't seem as familiar) and turned back.