Rome has a ton of old shit in it. There are thousand-year-old ruins awaiting your eyeballs literally around every corner, and you can't swing a porchetta without hitting the facade of a beautiful cathedral built when the years only had three digits. Looking for paintings that came from the hands of the Teenage Mutant Ninja Turtles? They're all over Rome, many of them in off-the-beaten-path churches and piazzas strewn throughout the Eternal City. But if you're interested in learning what life was like for Ancient Romans, your options are limited to The Roman Forum and a few other small sites throughout the city, as most of what remains from centuries past is constrained to the two G's of Ancient Rome-God or Government. If you're interested in what your average Orange Julius did on the daily, you're going to have to take a day trip, and most people will take the 2.5 hour, €60 train down to Pompeii. Then they'll pay €20 to enter the archaeological site, or maybe even spend up to €100 on a private tour, and that doesn't make sense if you're on either a time or money budget when you're in Rome. If you're on a trip to Rome with no budgets, by all means, spend your time in Pompeii, and also let's be best friends. But for most, a day trip to Pompeii is unnecessary when they could have gone to Ostia Antica.
Ostia Antica was the first seaport and naval base for the burgeoning Roman Empire and many consider it Rome's first colony, because it was so important to their military and economic growth due to it's strategic location at the mouth of the Tiber River. While the city flourished in the second and third century, it began to decline during the rule of Constantine I as the mouth of the Tiber naturally migrated away from the area. The name Ostia (the Roman word for "mouth") was no longer accurate, and as the naval seaport closed, the city fell into disrepair, eventually losing almost all of it's inhabitants and eventually being sacked of it's valuables: statues, paintings, and frescoes were removed by foreign explorers, even marble was chipped off the buildings and columns and re-purposed for other structures in cities both in the Roman Empire and beyond. While Pompeii was preserved quickly by the lava and ash of Vesuvius, Ostia was buried slowly by the economics and abandonment of Rome.
Ostia Antica, the site of the impeccably maintained ruins of this ancient city, are ridiculously easy to go to from Rome: a €1.50 Metro ticket (take line B to Basilica San Paolo, then the FC2 Lido to Ostia Antica, it's well marked at the station) is all you need to be transported to a place where it's easy to imagine Ostians engaging in their daily lives. There is an €8 entrance fee, but if you download the free Rick Steves Audio Guide before you go (In fact, I'd recommend using these audio guides throughout Rome, we used them for the Colosseum and the Forum and saved ourselves hefty tour fees), you won't need to pay for the audio guide or even a private tour. Strap on your headphones and jump into this ancient city.
You can run straight to what used to be a 4,000 seat theater and snap off some pictures at the top or on the stage, take a gander at the spectacularly preserved fresco which would have been on the floors of the baths, and chuckle at the novelty of a room which houses 24 ancient toilets side by side (complete with hole under the seat for your sponge-on-a-stick AKA Roman toilet paper to clean yourself after a nice chat with your buddies while you poop); or you can spend half a day touring the entire city, from the main square with it's frescoes depicting the wares of it's sellers to the necropolis which once housed the sarcophagi and urns of the citizens of Ostia to the far-reaching suburbs outside of town. There is no wrong way to explore Ostia, but if you're looking for an easy, educational, and off-the-beaten-path day trip from Rome, then Ostia Antica is the easy answer. It's never crowded (when we were visiting, there were maybe 150 other people in the entire town), and you can truly get a feel for how Romans went about their day-to-day life. We spent three hours there and felt that was a perfect amount of time, but everyone's interest/tolerance for ruins is different.
Check out some pictures from our visit below, and if you decide to visit Ostia Antica OR if you can figure out what those frescoes of the dolphin riders are, let us know in the comments below!