All banks and shops and most museums and ancient sites close on public holidays.
Many sites (including the ancient sites in Athens) offer free entry on the first Sunday of the month, with the exception of July and August. You may also gain free entry on other locally celebrated holidays, although this varies across the country.
National public holidays:
New Year's Day 1 January
Epiphany 6 January
First Sunday in Lent February
Greek Independence Day 25 March
Good Friday March/April
Orthodox Easter Sunday 28 April 2019, 19 April 2020, 2 May 2021
May Day (Protomagia) 1 May
Whit Monday (Agiou Pnevmatos) 50 days after Easter Sunday
Feast of the Assumption 15 August
Ohi Day 28 October
Christmas Day 25 December
St Stephen's Day 26 December