metro - Linea B to Piramide, Ostia Lido train to the Ostia Antica stop
Ostia is a short metro and train trip from the centre of Rome and was ancient Rome's seaport believed to have been founded in the 4th century BC.
It was originally at the mouth of the Tiber River but is now inland due to silting and a drop in sea level.
It is a large archaeological site with buildings, baths, temples, frescoes and mosaics and an interesting site to explore by yourself.
Buy a trusty guide book to help you find the major attractions.
It is great to be able to wander around, climb down into caverns (take a torch, good walking shoes, hat and sunscreen) and leave the paths and wander amongst the endless un-excavated ruins.
It takes hours to investigate Ostia Antica and there is also an on-site museum to visit.