The city is great if you have enough time to enjoy it. The big minus is that you have a 3 hours journey from where the ships anchors (Warnemunde) to Berlin and 3 hours to get back to the ship, leaving you little free time to explore the city. We only recommend it if its your only chance to see Berlin.
From the port its a 10 minutes walk to the Old Town. We didnt book a tour, before getting there we contacted the Tourism Office and they sent us home maps and a magazine with the town highlights. It was great to discover the city at our own pace. Also our ship was the only at port that day so it was not crowded. The knitting work is excellent quality.
We took a 2 days tour with TJ Travel. We suggest doing this city with a guide not only for the visa issue because they are really knowledgeable and in general Russian people dont speak English.
St Petersburg is a city of contrast, huge and luxurious palaces, churches and fountains and amazing art collection at the Hermitage Museum from the Tsars period with big soviet monoblock buildings. We had the chance of seeing also the Metro and a Farmers Market which helped us to understand a little bit of Russian history and culture.
We really enjoyed Helsinki. We took the 14B bus and the Tram to have a first impression. The Esplanadi Market is great to buy souvenirs (also the tax free at Helsinkis Port) and to eat local food. The Rock Church is a must see. Its easy to walk around and a good place to chill out after st petersburg marathon.
Another DIY city. We took the ship transfer and spent most of our day in the old town. We didnt go to the Vasa Museum however we visited the Nobel Museum, the Royal Palace and the City Town Hall. People is very friendly and this was one of our favourites port.