The primary terminal for both domestic and international flights at Athens International Airport (ATH) is where Ryanair is based. I just traveled with Ryanair, and I thought Terminal 1 was really efficient and well-run. There was good signage directing travelers to the Ryanair counters, making the check-in process simple. 
https://medium.com/@peterrpark....er099/a-comprehensiv
 
                
		 
		 
		