Literal translation
Who has seen Paris and not Cassis has seen nothing
Meaning
who has seen Paris but not Cassis has seen nothing
Explanation
Whoever has seen Paris but not Cassis has seen nothing works on three levels : literally, as regional pride asserting that the finest places lie in Provence rather than Paris, and finally as a general lesson, that one should not settle for a city's surface but go see everyday life in its distant villages.