and welcome to the forum.
It is a couple of years since I last visited the area, but then it looked like the Mare Nostrum was the main and all inclusive option in the vicinity.
In the valley south of Mare Nostrum there is a historical site with a museum surrounded by some marshey areas.
Going in the opposite direction (north) there are many nice coastal resorts. Going south and then passing the ridge you will be in Marcopolo which is close to Athens' airport.
I recommend hiring a car for independence when going around.