In the southern part of Italy, several cities and present day world heritage sites owe their founding to Greek colonists: Naples, Siracusa, and Agrigento are a few examples. Another is Paestum and the Vallo di Diano, situated 100km south of Naples. The overall area was also referred to as Magna Graecia and had Greek speakers well into the Middle Ages where it was still part of the Byzantine Empire.
Of the listed "Greeks in Italy" sites, Paestum is most like Agrigento. Both boast many great temple ruins. The main difference I would see is that Agrigento has the more stunning scenery with the temples located on hills overlooking the Mediterranean. The other noticeable difference is that different stones were used for the construction. The orange/brown/golden stones of Agrigento are just a site to behold.
I have to admit that I only visited Paestum and that the site contains more components. Most prominently, the site also includes a medieval monastery as this tries to cover to full time range of Greek settlement in the area. Still, Paestum is the jewel of the site and I would question the decision to include the larger area.
Getting There
Paestum has it's own train station connecting you to Salerno (north) and Reggio di Calabria (south). You can also connect eastwards and travel on to Taranto.
From the train station it's a short walk to the site. The first structures you will see are the massive walls running around the former town. It also gave me a good feeling for the scope of the site.
While You Are There
From Salerno, you can visit the Costiera Amalfatina. You can also travel on to Pompei and Naples. Salerno also boasts yet another fine Norman Duomo.
Note
Our GPS coordinates are misleading. They group several spots into a National Park and do not point to Paestum proper which is significantly further North.