I'm traveling with my 22 year old daughter. My plan is to take the train from port to Roma San Pietro so we can see St. Peter's Basilica. After that, our "must sees" are the Coliseum, Trevi Fountain, Spanish Steps, Pantheon. We, of course, hope to see much more, but we want to explore on our own. I've found a good self-guided walking tour. My question: what's the best way to get from St. Peter's over to where these sights are? I don't mind walking, but I am also mindful of the short amount of time we have on a cruise stop. Is one location better to get to first? We don't have tours booked. We are just seeing them from the outside. TIA!