Athens is about 29 times bigger than Cocos (Keeling) Islands.

Cocos (Keeling) Islands is approximately 14 sq km, while Athens is approximately 412 sq km, making Athens 2,843% larger than Cocos (Keeling) Islands.
Tip: This to-scale comparison of Cocos (Keeling) Islands vs. Athens uses the Mercator projection, which distorts the size of regions near the poles.