Our favourite stop of the five stops(Lisbon, Cadiz, Malaga, Cartagena)for history, culture, setting, and eating. Used private touring services from Trip Advisor site and had an exceptional time. I am sure the ships tour would have been fine but we prefer to be self-directed.
Impossible to find transport unless you were going to Rome. The shuttle to the port gates has a long line up but it will move quickly. If you are going to Rome, take the Holland America transfer as it will by far be the easiest. If you are going into Civitavecchia you will not be able to find a taxi so either pay the fee and be picked up at the port or gates, or be prepared to walk from the port gates.