My trips to Europe have been to Germany so I can't give advice on the cities you're visiting. I have been on 3 cruises and would mention though, that the cruises usually offer excursions you can take at each port. They are usually more expensive that what you can see to book yourself. However there is one advantage to booking from the ship, at least in our case (a Carnival ship) they guarantee to get you back in time for sailing, hold the ship, or get you to the next port. If you book outside the ship, and you get back late, you are on your own to get to the next port. This happened to us on an excursion in Belize, the bus blew a tire about 45 minutes out (we had gone to see some Mayan ruins) coming back. We had to wait for a replacement bus to come. We were to late for the last tender back to the ship, but they had a special (very fast) tender waiting for us with a ship security officer. The ship had turned around heading out to sea, and was waiting for us, and sailed as soon as we were onboard. As we got on, people at the rails were cheering, so I guess they announced they were waiting for us. We were very glad we had booked that tour through the ship.