We took the cab to Rostock last year because it was easier and the train station in Warnemunde was not located near where our ship docked. It's just a few miles and was very cheap. You may be able to take the train from Warnemunde to Berlin, and this is the site I've been using for years for Europe train schedules that I've found to be reliable and accurate: http://www.raileurope.com/us/rail/fa...ules/index.htm
. On our sailing last year, the Berlin excursion was a full-day tour and not a do-on-your-own. The hop-on hop-off bus might be a good option for you after you make the commute into Berlin.