During peak months, KD Rhine has as many as five ships cruising this section of the Rhine daily, and numerous smaller companies offer additional options. And you can certainly blend in train transport, either to fill in gaps or accelerate travel. For example, if you've finished with Lahnstein and want to explore neighboring Braubach (with the Marksburg, the Romantic Rhine's only hilltop fortress that was never destroyed), don't wait for the next boat; more frequent trains will get you there in six minutes. And then continue on to Boppard from Braubach. Local trains run at least hourly on both sides of the river. Just remember, there are no bridges across the Rhine between Koblenz and Mainz; so you'll have to depend on ships or ferries to get from one side to the other.

But what to do with luggage during the day, when you're exploring ashore? Even those who travel light will have to find a place to store their gear ashore. A €2 locker at a train station will hold two large suitcases for as long as 36 hours. If you've selected a restaurant for lunch, it may be amenable to storing your luggage for a few hours before or after. Finally, tourist offices are eager to help in any way they can. These are not large towns, and you'll usually find steamship stops, train stations and tourist offices all within close proximity.

Which kind of tickets should you buy? Remember, the total distance is less than 40 miles. By ship, the route from Koblenz to Bingen costs only €23.20 for an adult. Break it into two segments, say Koblenz-Boppard and Boppard-Bingen, and the cost is still just €24.60. For the train, second class from Koblenz to Bingen costs just €9. In two parts the price is €11.20. So the best bet is to go a la carte. Even rate hikes scheduled later this year for short distance trips aren't likely to increase fares much more than 10 percent.

Buy ship tickets each time before you board, and buy train tickets at the multilingual automats located at each station. (If you present the train ticket you just used when you buy a ship ticket at the KD counter, you'll get 20% off.) Bottom line: Though both German Rail and Eurail passes are valid for free passage on trains and ships of the Köln-Düsseldorfer line, you might not want to spend one of your pass's travel days on a short $20 boat ride.

There's another reason to travel by ship. Being on the river gives a strong sense of history and purpose. For example, you can see the castles in context. During the turbulent middle ages, they served as protection for bishops, nobles, prince-electors, robber knights and dukes. Many were also toll stations, each controlling their part of the river and collecting a percentage of the goods transported. At one time, a ship starting full in Bingen might arrive in Koblenz with only 10 % of it's goods remaining.