Holtsárfoss is a waterfall in the south of Iceland not far from the Skalavegur (road 246). From here it is a 2 hour walk
The river Holtsá runs from the glacier Eyjafjallajökull and not far from the edge of the glacier, Holtsárfoss falls from a cliff into a canyon. The waterfall is about 50 meters high.
I am not sure how the waterfall looks like, but it should be in the Holtsdalur.