We recently (May 2015) took this cruise with Viking which starts in Frankfurt and ends in Amsterdam aboard one of their very new long ships, the Eistla which first sailed in 2014. The cruise itself is a new version of a longer cruise along the Rhine (and the Main and the Moselle) which they only offer a few times a year. We used Viking air from Austin through Atlanta and straight to Frankfurt. The Eistla was docked right at the entrance to the old town (Romerberg) under the old iron foot bridge that crosses the main. This is an ideal location to access the old city, the cathedral and stroll up and down both sides of the Main.
From Frankfurt we sailed south to near Heidelberg and was bused into that city to explore the old town and the castle. Very picturesque and well worth a visit. From their we sailed north to port in Rudesheim for the evening. At Rudeshiem we walked the "acclaimed" Drosselgasse (a relatively narrow street with many bars, restaurants and "livemusik". I thought it worth the visit but a bit touristy.
The next day would be considered the highlight of the trip as we sailed north along the Rhine from Rudesheim to Koblenz. There is a 40 mile stretch with approx 60 castles lining the hills on both side of the Rhine - this is a UNESCO area site. After docking in Koblenz (the confluence of the Moselle and Rhine rivers) we head back south a bit to the Marksburg castle by bus. This is a very worth while side trip and the castle and the views of the Rhine from it are quick spectacular.
The next day in Koblenz we bused down the Moselle to the small town of Cochem with its own wonderful castle, the Reichsburg Castle. Cochem is charming and the castle perched above it is well worth the time. We also had an opportunity later in the day to walk Koblenz - not as much to do here but interesting walk through the town and along the Rhine and Moselle Rivers.
The next day found us in Cologne where we visited the incredible cathedral which reminds one of the cathedral in Barcelona - enormous Gothic cathedral that took hundreds of years to complete. Inside, the 3 wise men are claimed to be buried in a golden crypt.
Sailing north from there, our next stop was Nijmegen, The Netherlands. Here there is a large WWII museum dedicated to the US and British forces that helped liberate the area from the Germans. Quite large and impressive collection of weapons, ordinance, planes and tanks. We also walked old town Nijmegen - a bit hilly if you can believe but worth exploring.
The next day was Amsterdam where we both walked and rode the canals of the city. Port here is to the north east of downtown and very convenient walk to the train station or down town, the museum district, etc... We were fortunate to be in Amsterdam when Kukenhof Gardens was still open - the tulip display here is enormous (7M tulips?) as was the crowds. Beautiful grounds and shops and places to eat - you can spend an entire day here. Kukenhof is west of the city and opened only between March and May. A must visit in Amsterdam is the Van Gogh museum. All in all, we found Amsterdam delightful and extremely walkable.
We extended our trip in Amsterdam scoring a wonderful small hotel (The Aalders) centrally located in the museum/park area of Amsterdam. You could walk anywhere from here. The Aalders is within 2 blocks of a bus station where you can pick up a bus directly to Schiphol Airport for about 2 euros (20-30 minutes). The Aalders was reasonably priced at about 140 euros which included breakfast. Very close by is a full grocery store - one evening we bought bread, wine and cheese and made a meal of it in our room. Prices we found to be very reasonable for food and beverages in the local area - the local bakeries were superb for a lunch bite. My wife got to visit with an old grade school friend that lives just north of Amsterdam and we spent a day walking the dykes and visiting some of the smaller towns around Amsterdam. We would definitely recommend Amsterdam as a staring or ending point - very friendly, very walk-able and very reasonably priced. We will return.
The Eistla is one of 9 new long ships Viking launched last year - the rooms are small but well done, the ship quiet and smooth, the food was excellent as was the staff. No problems with water heights along the cruise but people taking river cruises should always be aware that rivers rise and fall (and flood) and the passage ways under some bridges are very tight. Fortunately you can find water depths along the river on line - the Eistala drafts only 1.7 meters so its a bit more adaptable to water depths than older ships. Also, the bridge can actually move up and down to make passing under bridges with high water easier. The Eistla carries 190 passenger
(we weren't that full) and a crew of only 50. Good trip - good value.