We had never been to Europe but decided before COVID that our first trip would be a river cruise. We chose Avalon because it seemed to include everything that we wanted in a vacation, including a great choice of excursions, plus additional options. The fact that we could add three days in London was a bonus.
Our expectations were exceeded. The entire trip, from arrival in Paris to departure in London, was seamless. The ship was great, the crew very friendly and attentive, the tours high-quality, and the food delicious. Our only additional expenses on the cruise were the tips (which I later learned could be pre-paid) and our drinks outside of meals (the bar tab for the two of us for the entire week was what I've spent in one night in the States).
The additional three days in London were supported by an affiliate, Monograms, and again we were well-supported with smooth transfers, a great optional evening dinner cruise and an entertaining and educational morning tour of London.