The Vienna Rathaus (city hall) was absolutely stunning all lit up.
The Christmas markets of Austria and neighboring countries were so pleasant and memorable. Walking around with all the lights, wares, smells and music was just amazing.
I went to the Salzburg markets as often as I could, whether it was to drink some Glühwein (mulled wine) or purchase a delectable snack or present. When there was snow it was that much better.