The Rhine Valley or Middle Rhine (German Mittelrhein) is the most famous section of the Rhine, running between the cities of Bonn and Bingen near Mainz in Germany and spanning the states of North Rhine-Westphalia, Rhineland-Palatinate and Hesse. The section from Koblenz to Bingen and Rudesheim, known as the Rhine Gorge, is a UNESCO World Heritage Site, and the entire valley is often called "The Romantic Rhine".
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.
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.
A large number of luxury cruise operators sail up (and down) the Rhine from Amsterdam to eg. Basel, Zurich or Strasbourg. The leisurely journey with plenty of stopovers typically takes anywhere from one to two weeks, with accommodation on the boat itself. Large operators include Avalon and Viking, with low-season prices for a 7-night cruise starting from around US$2,000.
The Koln-Dusseldorfer Rheinschiffahrt, better known as KD, runs cruises and scheduled services up and down the river between Cologne and Mainz. The summer season (May-Sept) sees up to 8 services daily on the busiest parts of the river, but services are cut considerably in the shoulder seasons of April and October and slow down to a trickle in the winter.
A riverboat cruise along the Middle Rhine makes a lasting impression. Sipping a glass of wine from the vineyards you are passing, enjoying the sunshine on the boat's upper deck and the castles passing by, you'll know what is special about the Rhine.