For Berlin, we booked our shore excursion through the ship. It was $325 per person to take a train to Sachsenhausen, then a bus to Berlin. A nice family-style lunch was included in Berlin, and several photo stops. And then a three-hour train ride back to Warnemunde and the ship. It's a long day - but absolutely worth it.
Train is not air conditioned! Be forewarned. It was almost unbearable.
Not much to see or do in Helsinki. We booked a Hop-On Hop-Off Bus Tour with City Discovery - with an out of synch tape. So that was confusing. Incorrect information from the tour operator kept us from seeing the Church in the Rock.