Booked a solo last minute trip to Athens Greece (in 3 days). Would love some recommendations

I've heard that Athens is good for ~3 days tops. So I'd like to ride that tourist trap to the floor and then go off and explore.

I'm into nature and want to get an authentic experience. I'm a 24 y/o male. I'd also love to learn more about Alexander the Great. Given it's winter I figured Mt. Olympus is out. I don't mind buying another flight to something nearby and back for part of the trip (Macedonia?). I went to Italy last year and spent a week in Rome and a week in a quiet town, Manciano. Both were absolutely wonderful.

I've also read about ferrying to some neighboring islands. So perhaps 3 days in athens, 3 days days at an island and the rest of the trip ???

I'd love any sort of advice. I should be traveling solo and got this last minute as I''m transitioning to a new job and have a break.

Departing to Athens 2/20 Return flight on 1/7 I'll have 14 non-travel related days free.