We will be going on our second Viking River Cruise this November. Your correct that it is very active with allot of walking. The age group is older than traditional cruising but, you need to be able to walk good distances with hills and steps.
We saw some guests stay aboard the Viking Longship. It was sad to see someone limited like this. We also saw some people struggle.
I joked i lost weight on my river cruise because the food was actually fairly healthy (no heavy sauces) with proper portions. My Samsung phone has a health monitor app that runs in the background. On our trip it started going crazy awarding gold coins daily for me for breaking my record for all the walking we were doing. The days were full and we slept well.
I would definitely recommend a Viking RIver Cruise. Please take a look at our Facebook Album from our Rhine Getaway:
Click Here