Another vote for Ravenna. The mosaics are extraordinary. All of the churches, baptismal fonts and the chapel on the "mosaics" group ticket are walking distance from each other in central Ravenna. The mosaics at the church in Classe are a short bus ride away -- the bus stop is in front of the train station. This is all explained in the Rick Steves guide to Ravenna. Ca de Ven, a restaurant recommended in the guide, is amazing. We asked for a platter of charcuterie, squacquerone cheese (a local soft cheese) and piadine, in addition to our lunch. For dessert we asked for the Rick Steves-recommended (and heavenly) almond/chocolate "brownie."
We used Bologna as our base for a weeklong trip to the Emilia Romagna region. Stayed at the Bologna UNA Hotel, which is near the train station yet very quiet. Great breakfast. We took day trips to Modena, Ravenna, Parma, Ferrara and Piacenza. Piacenza is further away on the Emilia Romagna train line (almost 2 hours away versus an hour for the other cities along the train line); it's closer to Milan than to Bologna.
Our visit to Piacenza was an unexpected trip highlight. We wanted to see the liver of Piacenza, an Etruscan bronze liver model used to teach seers in Ancient Rome how to "read" the livers of sacrificed lambs when predicting future events. The liver (fegato) is at the Civic Museum of the Farnese Palace in Piacenza. Also at the museum is the "Tabula Alimentaria Traianea," a very large bronze tablet from Roman times with the names of farmers who had been granted low interest loans in exchange for supporting children in need. Because there were very few visitors in the museum, we got a special tour. The docent showed us all his favorite items, sometimes taking us behind the scenes (secret passages inside the walls), until we finally arrived to the Etruscan fegato. Our lunch at Usteria la Carroza (near the train station) was as good or better than our museum tour.