Hellenikon International Airport served Athens from 1938 till 2001. It is located in the south part of Attica, in the municipality of Hellenikon (Elliniko).
After its closure (2001) some of its parts were used for the 2004 Summer Olympics (canoe/kayak slalom, field hockey, baseball, and softball) but the main buildings were left and still are unused. Now a part of the main building is used as a refugee camp, but all the rest is completely abandoned.
More info: flickr.com