It should have been obvious from the dozens of beautiful young men dressed in period costume who hawk concert tickets outside the main tourist attractions. Mum and I spent a good 10 minutes or more talking to a lovely young man outside Stephansdom.
The next clue should have been the Vienna State Opera, where I saw Richard Strauss's Salome. If this isn't the most dramatic, eat-your-heart out stage performance, hard to know what would be! (Think dance of the seven veils and the head of John the Baptist on a platter!)
Having made this connection, I really began to enjoy Vienna.