There are two international airports in Istanbul (which is 45 minutes far from Kocaeli):
- Ataturk International Airport: Atatürk International Airport is located at Yesilkoy district on the European side of Istanbul. In order to get to Kocaeli from Atatürk Airport, you can take the subway inside Atatürk Airport to “Esenler” Bus Terminal (ca. 20 minutes). At Esenler Bus Terminal, there are many bus companies shuttling from Istanbul to Kocaeli and vice versa. There, you can take one of the buses to İzmit Bus Terminal (Izmit is the central town of the province of Kocaeli).
- Sabiha Gokçen Airport: Sabiha Gokcen International Airport is located on the Asian side of Istanbul. From Sabiha Gökçen Airport you can take HAVAŞ shuttle buses to İzmit Bus Terminal. For updated information on shuttle hours, please visit the following link: http://www.havas.net/en/shuttle-parking/istanbul-sabiha-gokcen-airport/