When to go
The peak season is definitely summer, when the hillsides are green and the cruise boats busy. In September, many inns and restaurants already start closing down for the winter, and almost all cruises end by November, starting up again in April.
Understand
The Rhine Valley, where the Rhine carves its way through steep hills topped with countless castles and ruins, is one of the most famous and most heavily touristed parts of Germany. Traveling here is very easy — cruises, castles and winery tours by day, sampling the wine at night — and it's no surprise that the visiting demographic is slanted heavily towards retirees looking for an easy break.