Ostia Antica is one of the most incredible—and underrated—archeological sites in Italy. The ruins of Ostia Antica date from the 2nd century when it was a bustling port city, with ships coming from all over Europe and beyond. As you wander around, you’ll see the ruins from the forum, amphitheaters, apartment buildings, taverns, shops decorated in mosaics and the oldest synagogue of the Roman Empire. Spend at least half a-day here. You can get a taste of it in three hours. But you would need to stay all day to take it all in.