River cruises are wonderful! Did part of the Rhine some years ago, from Cologne to Basel. Beautiful! And only 100 passengers.
Mom and her friends have done the Rhine, the upper and lower Danube, the Nile, and some others. They’ve done some trips on big ships, like the Alaska cruise-and-train tour, but decided they liked river cruising better.
Back in the late 80s when I was in England, I looked into doing a cruise down the Nile. Unfortunately, that was when the Islamic Brotherhood was murdering tourists, so I canned that idea.