When the usual sites in Rome are heaving with people, Ostia Antica is a place of superb Roman sites which are blessedly peaceful. The site was once the sea port of ancient Rome but was silted up after the decline of the Roman Empire. Many buildings have been excavated and it is possible to spend a whole day here enjoying the sites and rural peace. We were there on a Saturday and it was not mobbed like the centre of Rome.
Google map: bit.ly/Aet2ld