From the direction of Munich:

Take the motorway A8 Munich Salzburg to the exit Inzell, then via Lofer, Saalfelden turn left to Maria Alm. With this option you do not use an Austrian motorway and therefore you do not need a motorway permit sticker. 

From the direction of Vienna:

Take the A1 Vienna-Linz-Salzburg motorway and then the A10 towards Villach until the exit Bischofshofen. Then continue towards St. Johann, on to Zell am See and through the tunnel at the beginig of Zell am See, then continue in the direction of Saalfelden. In Saalfelden turn left and after about 10 kilometers you will reach Maria Alm.

When you arrive in Maria Alm, you have to drive through the village and follow the Krallerbach on the right-hand side (about 2.5 km). At the end of the valley you will have reached your destination. :-)