This new service is great news:

The 400, a new public sightseeing bus line, with 20 stops at major Athens museums and monuments, will operate between 7:00 and 21:00. Buses will run roughly every half hour, the entire journey lasting 80 to 90 minutes. Passengers will be informed regarding the various stops via recorded messages in Greek and English. The ticket, costing 5 euro, will be sold on the bus. It will be valid for 24 hours for unlimited journeys on all Athens-area public transport (excluding airport services).

Cheers! Linda