Safety at night:Safe
Kythnos, like most Greek islands, is generally safe. Locals are friendly and quite helpful, often going out of their way to assist tourists. Nonetheless, even though violent crime is very infrequent, it's not entirely nonexistent. Petty theft can still be an issue, particularly if you leave valuables unattended. Also, the island tends to be fairly quiet at night outside the peak tourist season, resulting in fewer people around in some areas. So, it's always a good idea to stay aware of your surroundings when wandering around alone at night.