Ostia Antica was the harbor city of ancient Rome. It is now a well-preserved archaeological site, about about 18 miles northeast of the city and 2 miles from the Mediterranean. It is a popular tourist destination due to its ancient buildings, frescoes, and mosaics. It’s also easily reachable from Rome via a 1/2 hour train ride and is only a few km from the airport. Ostia Antica makes for a good running option along its ancient roads. The stone surface is similar to the Appian Way, although there is grass/dirt on the side as well. It is about 1.2 miles from one end to the other in the Ostia Antica site (admission required). There are numerous add-on options. There are lovely farm fields on either side of the Antica site. Or, run to the sea, about 2 miles, and then along the water, where there is a separated bike path from Faber Beach to the port, and then a nice jaunt out to the harbor.