Eva, please accept my apologies if I repeat anything that's already been said.
We did the GAS tour last year and it was AMAZING. We were especially amazed by the Switzerland part of the tour. It was our fourth RS tour and it may have been the best (although I might just think that because it was the most recent). We have already booked tour number 5.
We spent two nights in Bacharach (Rhein Hotel) before the tour started; it broke up the travel between Frankfurt and Trier, and gave us a chance to see one of the most scenic stretches of the Rhine. Bacharach is about an hour north of Frankfurt by train, and Trier is about two hours from Bacharach by train (with a change in Koblenz). The two nights in Bacharach allowed us to take the boat ride up to St. Goar where we had lunch and browsed in the shops. For dinner, we dined at Stuber's, which is a fine restaurant in the Rhein Hotel.
While in Bacharach we stopped at St. Nicholas Catholic Parish Church but it was locked. A lady in the bookstore attached to the church was kind enough to unlock it for us, and we had the inside of the church all to ourselves for a few minutes.
After the tour, we spent one extra night in Vienna, and spent the day at Schonbrunn Palace.