Kenneth and I did a Viking River cruise for the Xmas markets years ago...as in '05 or '06. Kenneth loved Xmas and it was a very special cruise...enjoyed the markets, the mulled wine and the entire 'holiday vibe". We ended in Vienna on Xmas Eve and then took the train a couple of days later to Budapest. That was just like a scene out of Dr. Zhivago with snow on the hay bales!!
They had older ships then and the Capt didn't speak English. When Kenneth ordered something hot for breakfast on the morning of disembarkation we were told they were not serving a hot breakfast because the cook was helping load the luggage!! I'm pretty sure things are a bit different these days!! 🙂 But I think you would love the experience.