Churches and monasteries
Cover shoulders and knees in churches and working monasteries; Meteora's monasteries lend wraps but expect you to know. Keep voices low, and never photograph the altar or services without permission.
Mount Athos is men only, with a permit (diamonitirion) arranged in advance. Women cannot enter the peninsula, including by boat close to shore.
Eating and tipping
Dinner starts late: 9 or 10 pm is normal, and tavernas fill after 10 in summer. Bread and water arrive by default; raki or dessert often arrives on the house.
Tipping is modest: round up or leave 5 to 10 percent for good service. It is appreciated, not obligatory.
Coffee is never rushed. A Greek coffee in a kafeneio can legitimately last an hour.
Daily life
The afternoon quiet hours (roughly 3 to 5:30 pm in summer) are real in villages and small towns: keep noise down.
Greeks are warm and direct; a little Greek goes a long way. Kalimera (good morning), efharisto (thank you).
Bargaining is not the norm except at flea markets; prices in shops and tavernas are fixed.