Clean Monday is a full official public holiday in both Greece and Cyprus, and in Athens the outdoor kite-flying custom concentrates in specific well known open spaces, most famously the hill of Filopappou opposite the Acropolis, where large crowds gather each year for a day that combines a genuine day off work with the informal atmosphere of a public festival, a level of civic recognition and popular outdoor celebration that a specifically penitential and abstinent first day of a fast might not obviously suggest to an outside observer.
Most other Orthodox countries do not treat Clean Monday as an official non-working public holiday at all, so the strongly festive, family-outdoor character the day has in Greece and Cyprus specifically is a national and cultural variation on the underlying Great Lent observance rather than a universal feature of how Orthodox Christians everywhere begin the fast, illustrating how the same liturgical starting point can be marked with a full day of public kite-flying and seaside picnicking in one country's civil calendar and pass as an ordinary Monday at work and only an evening service at church in another Orthodox country nearby.
The Great Lent that Clean Monday opens runs for forty days but does not, in the Orthodox reckoning, count straight through to Pascha: the forty days conclude on Lazarus Saturday, the day before Palm Sunday, and Holy Week itself is kept as a separate, more intensely fasted period layered on top of the forty, so that the season between Clean Monday and Pascha as a whole considerably outlasts the strict forty days the name Great Lent literally denotes.