One evening a few years ago, my wife, Fyllis, and I were savoring a sumptuous four-course gourmet dinner accompanied by wines that had been produced nearby. More recently, we listened raptly to lectures by knowledgeable experts about a variety of issues, some controversial, in several Eastern European countries. The settings for these experiences could have been a five-star hotel or resort, and indeed in atmosphere and attractiveness they deserved that rating. What set them apart was that they took place on small ships plying some of the most famous and fabled rivers in the world. At present, a number of oceangoing ships have been canceling sailings and, in some cases, dealing with an outbreak of coronavirus among passengers and crew members. That can be frustrating for the many people who love to take to sea. But there is an alternative that allows frustrated mariners to leave terra firma, enjoy a …