Rosemary, I noticed that no one has answered your question about optional tours, so here goes. We took this trip in July, 2010, during the worst heat wave in decades in Germany and Austria. At least it cooled down when we got to Amsterdam!
1) Melk Abbey- In cooler weather, we would have walked the two or three kilometers from the river up to this Abbey and just paid for our own admission, but considering the 95 degree heat, the transportation cost in the GCT package was worth every penny. We loved the tour of the buildings, the cathedral, and the library, and down in the basement there was a special exhibit about the architect that my engineer husband enjoyed a lot. Our charming young guide had gone to the Abbey's sister college, St. John's in Minnesota, and he spoke excellent English and gave interesting commentary. The gardens and forest were lovely, and we loved the serene greenness of that area, especially in the heat. Be sure to allow time for the outdoor areas.
2) Baroque and Beer- The Baroque church is in such contrast to the architectural styles of other churches we saw in Austria and Germany, and we both thought it was fascinating and beautiful. The guide inside the church did an excellent job of explaining the decorations. We had pretzels and beer under trees, in a picnic area, and then boarded a small ferry for a ride on a scenic part of the river, back to our bus, which then took us to see the huge, ostentatious Liberation Hall. The whole trip was very pleasant and interesting, and we would do it again.
3) Rothenburg Tour- This all day trip was long but fun; how many chances do you have to see a 14th century city? The half timbered houses reminded us of something from Disneyland, and the surrounding city walls were massive. Half the day was guided, so we learned the history of the city, and the other half was free, so we enjoyed wandering about on our own, and also did some shopping. We were lucky to happen across a choir concert in one church, and sat for a bit and let the music envelop us. Some people on our tour had been to Rothenburg before, but I noticed that they chose to go a second time! This city is a tourist destination for folks from all over.
4)Rudesheim Dinner Outing - We didn't take this, for the food and wine on the ship was quite good and we already felt stuffed!
5) Marksburg Castle- This 13th Century Castle was a fun experience, and we would recommend it for any able-bodied traveler. There was some climbing of stairs and a lot of uneven spots, and I would not take this optional tour if you need a cane or walking aid, or have balance problems or problems with stairs. It was interesting to think about what life was like for the inhabitants so many centuries ago, to climb the towers and look out. The twelve year old boy who was with us really loved this optional trip, so if you have teens or kids with you, be sure to do this one. The second part of this trip was beer and sausages at a casual, fun brewery; the people (my husband, for instance) who loved beer and sausages were in heaven, but I, personally, would have been happy to just end the trip after the wonderful castle.
6) Amsterdam- Just on the street near the boat dock is a shuttle stop where, for about $2, you can get a ticket on a shuttle that drives all about Amsterdam to a lot of different sites. One of them is the Hermitage Museum. (It doesn't go as far as the Rijksmuseum, though. ) When we were tin Amsterdam, theHermitage Museum was having a special Matisse exhibit that I really wanted to see. (There are rotating exhibits, so look on-line before you go so you will know if they have something you are interested in.) After seeing that museum, we walked the pleasant mile to the Rijksmuseum.and enjoyed the hours we spent there before taking a $10 taxi back to the ship. The Van Gogh Museum is just at the other end of the park, and if we had wanted to go to those two (the Rijksmuseum and the Van Gogh) we could have done those instead, using a taxi both ways for less than the optional tour. You would still have to pay your own admission to whichever museum(s) you would choose to visit. We wanted the maximum time at the museums and on the streets of this lovely city, and this plan worked well for us.There is good shopping at the stalls in this grass area between the two museums, by the way.
So, Rosemary........I don't think you can go wrong with any of the optional tours we took, and we would choose to take all of them again! Have a wonderful trip.