From the airport:
Take the airport bus to the Western Train Station ("Westbahnhof"), then the U6 underground line (direction "Floridsdorf") and go just one stop to "Burggasse/Stadthalle". From there, you walk in the direction of "Zentrum" (city centre) for approx. 5 minutes and you are in the Halbgasse. Follow the yellow signs "Alla Lenz".
From the Western Train Station:
See above.
From the Southern Train Station:
Take tram line 18 to the end of the line ("Burggasse/Stadthalle"). From there, you walk in the direction of "Zentrum" (city centre) for approx. 5 minutes and you are in the Halbgasse. Follow the yellow signs "Alla Lenz".