For this achievement the player will need to discover all Italian cities. This means that the map of the city must turn from grey to yellow due to the player driving in or near the city.
The Italian cities are:
Ancona, Bari, Bologna, Cassino, Catania, Catanzaro, Firenze, Genova, Livorno, Messina, Milano, Napoli, Palermo, Parma, Pescara, Rome, Suzzara, Taranto, Terni, Torino, Verona, Villa San Giovanni
The 1.11 update added:
Venezia
The 1.35 update added three extra cities:
Cagliari, Olbia, Sassari
When you discovered all 26 cities, the achievement should unlock.