Pegasus Airlines is a Turkish low-cost airline that operates regular flights from Istanbul Sabiha Gökçen Airport (SAW) to Athens. SKY Express, based in Greece, also offers flights from Istanbul to Athens and other cities in Greece. These airlines are generally the main options for travel from Istanbul to Greece. However, the frequency of flights and routes may change from time to time, so it's important to check the airlines' websites or travel agencies for the latest information on your travel dates.