Upvote:2
Since you've been granted a Schengen visa with multiple entries, you're entitled to the Schengen Area Agreement that gives you the absolute freedom to go around the SA countries demonstrating that you follow the intended purpose of your visa and restrictions or staying and/or committing illegal activities there.
Upvote:3
As Layth pointed out, the Schengen authorities gave a multiple entry visa for your and their convenience, they found you trustworthy enough that they don't want to be bothered by you for every single entry. Your visa is valid for all Schengen states.
Think through your proposed trip as if you were preparing a new visa application.
When you arrive at Vienna airport, you should be able to explain this information in a coherent way. That would be easier if you had hotel reservations all the way, but enough money on hand can compensate for that.