Krossárfoss is a waterfall in the South of Iceland, appr 40 kilometers east of Kirkjubæjarklaustur along road 1. Driving from Kirkjubæjarklaustur to Núpstaður, Krossárfoss is located by the farm Rauðaberg about 2,5 km before Núpstaður. It is a short walk to the fall, about 600 meters.
Often Krossárfoss is mistaken with Foss a Sidu which is located 20 kilometers west of Krossárfoss. But I think the photo’s on Internet are not the Krossárfoss. Viewing google street view it is impossible that this is Krossárfoss.