The St. Stephens Cathedral, inside (with a temporary artistic light installation) and out.
The food - the notables: cheese at the decadent Meierei in Stadtpark, the best soups and broths in the game, and some serious meat and potatoes in all forms (goulash photographed).
The museums: Mumok for some quick views of modern art. But the real win was the Belvedere Palace with the Klimt paintings (no photos allowed inside).
The Schonbrunn Palace and all of its displays of the Habsburg monarchs (throughout 1,441 rooms, no big deal).
The Mozart Ensemble orchestra in the Mozart House, the oldest concert hall in Vienna where Mozart used to work, play and live!