My favorite way of travelling now that I am no longer a young person is River Cruising. No hassle, no getting up at the crack of dawn to have your luggage outside to catch the bus for the next City.
I have done 3 of the trips I am now enjoying, and if you want to see lovely towns, villages, as well as major cities, this is the way to go.
Viking has done a wonderful job on the two trips I have taken with them.
Staff on board, helpful and friendly, sightseeing tours just long enough to have you flavor the City or Village you are visiting.
Food more than satisfactory.
Only criticism I have is that I would enjoy a little more activities on the ships while sailing between different ports, especially if the cruise is a bit longer between points.
Viking seems to attract very interesting clients, and I personally look forward to joining them again on another trip.