I’m the one who booked the Belgium Markets in 2023 with Uniworld. It really seems unique as well as Taucks. I’ve previously sailed the Danube for Christmas Markets starting in Budapest and ending in Passau. We did a 3 day stay in Munich pre cruise and really enjoyed their markets. Budapest, Vienna, Bratislava, and Passau all had unique and fun markets. Plus there was a day trip to Salzburg. Highly recommend this itinerary. I’ve sailed the Rhine but not during Christmas. I really don’t believe you can make a mistake with either. Good luck in your research