Anyone take cruise to Italy ?

hi, I would like to know if anyone take the cruise to travel in Italy ? I like the tour with NCL , 11-Day Western Mediterranean Round-trip Rome (Civitavecchia) in December, but it seems like the local shore excursions are taking almost 8 hours everyday , it will be very tiring, right? Is anyone can tell me if I can just walk around the local, take taxi, instead of taking the cruise company's tour ?
Please advise.
Thank you !