Coming from Salzburg on the motorway A10 (Tauernautobahn), take the turnoff "Bischofshofen".
Continue on the dual carriage way (311) until St. Johann/Pongau.
There, turn off right onto the main road to Grossarl.
After about 10 km you will reach the center of Großarl,
another 8 km into the valley and you'll reach "the national park municipality of Hüttschlag".

Train station St. Johann im Pongau or Bischofshofen.

Continue by bus or taxi to Grossarl.

Further information on current schedules and connections, see the following links:
Österreichische Bundesbahn
Deutsche Bahn

Airport Salzburg
From there continue with train and / or bus and / or taxi.