If you want to spend some time in Ancient Ostia (outside of Rome), about how much time should you allow, how long does it take to get there and is it open on Sunday?
I would allow at least a half day. It is similar to Pompeii but was buried by mud and now has been restored. It is very interesting. Your can reach it in about an hour from Rome via public transit, one train change. Don't know about Sunday.
I went on a Sunday - but best to check the schedule:
http://www.ostiaantica.beniculturali.it/en/orari-ostia-antica.php Glenn
If memory serves correctly, the train leaves from the Piramide station which is a combination metro and train station. I would try to get an early start and be there when it opens as it will get hotter as the day goes on. About an hour each way and 3 to 4 hours to really explore the site. TC