Sea Turtle Rescue Society Archelon
Near Athens in Glyfada 50 min by tram from the center, there is the Sea Turtle Rescue Society Archelon. They are regularly looking for volunteers who are willing to work on their own costs and are able to take care of injured sea turtles. (http://www.archelon.gr/en...)
Athens and Epidaurus Festival
Attend an event at the Athens and Epidaurus Festival (http://greekfestival.gr/). It runs during the summer and offers a wide spectrum of events covering almost every taste. Try to attend a performance at the ancient theater of Epidaurus -a truly unforgetable experience.
free bike tour
Every Sat/Sun you can join a free bike tour of the old area of Athens. To take part in this, you should contact the NGO Anthropos (http://anthropos.gr) or call 210 8838914 but you can just turn up if you aren't able to contact them in advance. Groups meet at 10:40AM outside Thissio metro station.
EasyCruise
Syngrou avenue 362, kallithea , 176 74 athinai, phone +30 211 2116211. the infamous cheap flight company now runs a variety of cruises from greece [athens] to turkey and surrounding islands such as mykonos, paros and syros. for the classic enthusiast, their tour company visits acropolis, epidavros, nemea, mycenae, corinth, olympia and delphi.
beaches to the south of Athens
If the weather is good, head out of town on buses A2, B2 or E22 from metro station Sygrou, or the tram from Syntagma to the beaches to the south of Athens. Just get off wherever the sea takes your fancy. Be aware though that beach-side cafes can hit you hard with prices of food and drinks. If you are the only person getting on the bus, be aware that you need to flag the bus down to get it to stop or it will just fly on by.