Thanks Joe for your comment. We purchased 2nd class train tickets on the internet and have already received them. Warnemunde to Rostock then Rostock to Berlin. The train station you want in Berlin is the Zoo......... The tour buses are within walking distance to there at the Europa Center. You can buy the tickets at the Tourist Center there. It looks pretty straight forward and I can't believe that the German trains don't run on time!! We'll take our chances.