A Christmas markets cruise on the Danube River isn't quite the same as the usual spring, summer and autumn voyages. Mostly what's unique about this itinerary, available only in late November and in December, is centered on visits to the region's medieval Advent markets rather than vineyards or boat tours or languid walking jaunts around ancient villages. There's also the weather.... When I flew into Nuremberg to join AMAWATERWAYS' 148-passenger Amalyra for a pre-Christmas jaunt to Regensburg, Passau, Linz, Melk, Vienna and Budapest, the weather was numbingly cold. And yet the snow really did transform each city into the winter wonderland promised in the brochures. I can't think of a better way of getting into a festive mood. But having enjoyed Rhine and Danube River voyages in warmer seasons, I did have some trepidation. Would Christmas market fatigue set in? And with darkness falling at 4 p.m. and with shipboard life essentially taking place indoors, with only one lounge and one restaurant for everybody, would I get bored and restless?