The 8-working day Vienna Vibe cruise from U by Uniworld is a good alternative (note the cruise line is on hiatus right up until 2023). This cruise line was at first designed to cater to millennials, which itinerary contains excursions like a strolling tour of Vienna and biking around Passau. https://stephenfmmno.blogolize.com/the-definitive-guide-to-singles-cruise-2023-57092948