From Mauterndorf avoid signs to the autobahn and head up over the Radstadter. The high point is 1793m above sea level at Obertauern. Road generally wide and easy to pass outside peak holidays. Road popular with cyclists and mobile-home (RV) types!
Great road along the side of a lake, you can make it to Jaca from Bilbao in a day which is a good place to explore the pyrenees from.