Kocaeli Peninsula
Turkey
The Kocaeli Peninsula (Kocaeli Yarımadası) lies in the northwest corner of Anatolia, Turkey, separating the Black Sea and the Sea of Marmara on the Asian side of the strait of Bosphorus. Approximately one-third of Istanbul, one of the most populous cities of the world, occupies its western part, and İzmit, another big city, is at the easternmost point of the peninsula.
Data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).