Princess Excursion in Rome

#1
We are sailing on Royal Princess in September, and are a little frustrated by Princess' lack of knowledge about their own excursions. (I know they contract local companies....but still)

In particular, the "private train" into Rome. Is it a private train? A private car on a scheduled train? We are meeting a driver at St. Peter's station and he would like to know when we're getting into Rome.

Has anyone done this particular excursion? Any advice? Feedback?

Thanks.