Even on a tight schedule, Day Trip to Ostia Antica earns the hours.
Allow Half-day (4–5 hrs).
A sprawling, walkable Roman port town — paved streets, a theatre, mosaic-floored baths, multi-storey apartment blocks, and old taverns with their counters still in place — that you can roam almost alone, 30 minutes from the centre on a commuter train. It gives you the Pompeii experience (a whole city, not just monuments) without the all-day haul or the crowds, which makes it one of Rome's best-value half-days for anyone who wants to actually wander ancient streets.