Kocaeli is mostly known by its district center, Izmit. The ancient name of the city is Nikomedia. Remains from Roman and Byzantine times may be seen here, among which are the citadel, the Temple of Augustus and the agora. There are lots of harbour facilities within Kocaeli, including the primary base of the Turkish Navy.
The city of Izmit is mainly an industrial center in Marmara region of Turkey with numerous industrial establishments surrounding the Gulf of Izmit. However, there are also many tourist sites in this bustling province. Kartepe is a winter sports resort that reaches a height of 1600 m, Kerpe and Kefken on the Black Sea coast have fine beaches, while Golcuk and Karamursel in the Gulf of Izmit are other beautiful sea resorts.