Just to add Lynn, on Easter Saturday and Easter Monday specifically, opening times for arch sites and museum will revert to winter reduced times.
Athens is a huge cosmopolis, similar to Sydney in many ways {regarding pop/size}, there will be places open especially in the historical centre, but it will be unusually quiet as many of the Athenians will be away as Thalia added. If you want to experience some of the religious festivities, you can attend Easter church services on Good Friday and Easter Saturday.
If you and in or around Filipapou/Pnyx Hill {by the Acropolis} on Good Friday then you could attend a very traditional service at 12th c. Byzantine St Dimitris Loumbardiaris, which ends with the procession of the Epitaph along the Acropolis on Apostolou Pavlou, which then meets up with the other one from the beautiful Ag Marina church.
On Easter Saturday, from the Cathedral of Athens in Mitropoleos street, the Archbishop officially announces the rebirth> major fireworks and firecrackers follow.
Alternatively if you decide to leave Athens, make sure you make al the relevant bookings well in advance,
Edited: 11 years ago