Probably the most distinctive feature on the Ruby Princess is the large Piazza, which serves as the hub for all sorts of dining, drinking, and other shipboard activities, including "street" performers. There always seems to be something interesting happening in the Piazza, and the nearby International Cafe is filled with passengers most of the day.
Other popular areas are the theaters and the lounges. For those who like to stay active and fit while at sea, the fitness center has all the latest equipment, and the Lotus Spa is lovely.
Of course, since 900 of the staterooms have a balcony, maybe the best place to be is in your quiet cabin with a loved one. After all, Princess is the original Love Boat!