Opening Hours of Museums and Archaeological Sites in Greece

I will try and update this as often as possible. If you find any information that is erroneous, please let me know. Please verify the information BEFORE visiting the site!

NOTE: Unless otherwise stated:  
Winter: From the 1st of November 2013 until the 31st of March 2014
Summer: From April 1st, 2014

ATTICA
Athens

• Acropolis of Athens, Theatre of Dionysus (Acropolis South Slope), Ancient Agora of Athens: Summer: 7/7 - 08:00-20:00
• National Archaeological Museum, Athens: From Summer: 7/7 - 08:00-20:00 Archaeological Site of Olympieion, Athens: Summer: 7/7 - 08:00-20:00 
• Benaki Museum, Main Building: Wed., Fr.: 9:00 - 17:00; Thur., Sat.: 9.00 - 24.00; Sun: 9:00 - 15:00
  
• Benaki Museum, Pireos St. Annexe: Thur., Sun.: 10:00 - 18:00; Fri., Sat.: 10:00 - 22:00
• Byzantine and Christian Museum, Athens: Summer: 7/7 - 08:00-20:00 
• Kerameikos: Monday-Sunday: 08.00-20.00

Rest of Attica

• Archaeological Site of Sounio: Summer: 7/7 - 08:00-20:00

MACEDONIA

• Archaeological Museum of Thessaloniki: Summer: 7/7 - 08:00-20:00
• White Tower, Thessaloniki: Summer: 7/7 - 08:00-20:00 
• Museum of Byzantine Culture, Thessaloniki: Summer: 7/7 - 08:00-20:00
• Royal Tombs of Aigai (Vergina): Summer: 7/7 - 08:00-20:00

PELOPONNESE

• Archaeological Site of Epidaurus: Summer: 7/7 - 08:00-20:00
• Archaeological Site of Mycenae: Winter: 08:00-15:00: Summer: 8:00-20:00.
• Archaeological Site of Olympia: Summer: 7/7 - 08:00-20:00 
• Museum of Ancient Olympia: Summer: 7/7 - 08:00-20:00
• Archaeological Site of Mystras: Summer: 7/7 - 08:00-20:00
• Palamidi Fortress, Nafplion: Summer: 7/7 - 08:00-20:00 
• Archaeological Site of Ancient Messene: 7/7 - 08:00-20:00
• Museum of Ancient Messene: 7/7 - 08:00-20:00

CENTRAL GREECE

• Archaeological Site of Delphi: Summer: 7/7 - 08:00-20:00
• Archaeological Museum of Delphi: Summer: 7/7 - 08:00-20:00

CYCLADES

• Archaeological Site of Delos: Summer: 7/7 - 08:00-20:00
• Archaeological Site of Akrotiri, Santorini: Summer: 7/7 - 08:00-20:00

DODEKANESE

• Sanctuary of Asklepios on Kos: Summer: 7/7 - 08:00-20:00 
• Castle of Neratzia, Kos: Summer: 7/7 - 08:00-20:00
• Archaeological Site of Lindos, Rhodes: Summer: 7/7 - 08:00-20:00 
• Archaeological Site of Kameiros, Rhodes: Summer: 7/7 - 08:00-20:00 
• Archaeological Museum of Rhodes: Summer: 7/7 - 08:00-20:00
• Palace of the Knights, Rhodes: Summer: 7/7 - 08:00-20:00 
• Acropolis of Ialyssos, Rhodes: Summer: 7/7 - 08:00-20:00
• Archaeological Site of Ancient Corinth: Summer: 7/7 - 08:00-20:00

CRETE

• Archaeological Site of Knossos, Crete: Summer: 7/7 - 08:00-20:00 
• Archaeological Site of Phaistos, Crete: Summer: 7/7 - 08:00-20:00 
• Psychro Cave, Lassithi, Crete: Summer: 7/7 - 08:00-20:00
• Spinalonga Islet: Summer: 7/7 - 08:00-20:00 
• Archaeological Museum of Heraklion, Crete: Summer: 7/7 - 08:00-20:00

IONIAN ISLANDS

• Old Fortress of Corfu:  Summer: 7/7 - 08:00-20:00 

THRACE & ISLANDS OFF THRACE

• Thasos Archaeological Site: Summer: Tuesday to Sunday 08:00-20:00. Monday: closed 
• Archaeological site of Thasos: 08:00-18:30. The ancient theatre is closed due to reconstruction.