On the A10 (Tauernautobahn) take the extit "St. Micahel im Lungau" or on the B99 you will come to Obertauern. In both cases you have to drive to Mauterndorf, followed by Mariapfarr.
From Vienna drive to Judenburg and Unzmarkt, followed by Murau, Ramingstein, Tamsweg and finally to Mariapfarr. You can also take the A1 (Westautobahn) to Salzburng and take the A10.
From Villach you have to drive through the Katschbergtunnel to St. Michael im Lungau – Mauterndorf – Mariapfarr.