Rick Steves says of the cost of visiting the Ara Pacis: "€11, more with special exhibits, tightwads can look in through huge windows for free, daily 9:30-19:30." We chose to be tightwads and just looked in the windows, which as you can see wrap around all sides of the altar and give a pretty good view. I'm really not sure it's worth €11 just to get a closer look, but to each their own. We were kind of bored of ruins anyway at this point.