Hjálparfoss Waterfall in Thjosardalur (Þjórsárdalur) is situated just before the road takes you into the Southern Highlands and is easy to access from the main road. It is a beautiful place, the double waterfall, the lagoon and some interesting lava formations make it a place you should definitely not leave out if you are in the area. It is more than worth the while to hike down the short footpath to the river although the view from the parking place is great.
There are some very interesting places to visit in Thjorsardalur Valley and you should not pass them by. One of these is Gjáin, not far from Hálparfoss.