Visitor center at Michaelerplatz in the Hofburg (under the Michaelerkuppel):

Michaelerplatz 1, A-1010 Vienna
Tel: +43 1 533 90 31-0
Email: office@srs.at
 

opening hours:

Monday: 12:00 until 16:00 hrs
Tuesday to Sunday: 09:00 until 16:00 hrs

Entrance and cash desk at Josefsplatz:

Josefsplatz, A-1010 Vienna

Until further notice the cash desk is closed