Italy and Sicily are very popular, especially with Monarch and the Greek Islands not yet much on the map - although Athens was then a big charter destination for both holidays, and to join cruise ships.
I flew down to ATH several times with BY in the early 80's. At that time many of the airports on the popular smaller islands could not handle jet traffic (so a lot of holidaymakers ended up traveling on ferries via ATH which was indeed very busy with charter traffic)