Heybeliada

Heybeliada, or Heybeli Ada, (Greek: Χάλκη) is the second largest of the Princes' Islands (Adalar) in the Sea of Marmara, near Istanbul, Turkey. It is officially a neighbourhood in the municipality and district of Adalar, Istanbul, Turkey. Its population is 4,424 (2022). Its name, meaning 'with a saddlebag' in Turkish, is supposed to refer to the valley between two hills.

The island was known as Halki, Halkitis (Greek: Χαλκίτις) and Demonesos (Δημόνησος) in antiquity, the first two toponyms deriving from the Greek word halkos (Greek: χαλκός), meaning copper. The island was famous for its copper and copper ores in antiquity.

In winter, the island's population is approximately 4400, but in summer, when owners of summer houses return, the population swells to approximately 30,000.

Launched in 2008, TCG Heybeliada, used by the Turkish Navy is named after the island.

Until 2020, the only vehicles permitted on the island were ambulances, fire tenders, and police vehicles. The only official form of transport was by horse-drawn phaeton. However, as tourism steadily increased, animal rights activists became increasingly concerned about the horses' welfare, and so the phaetons were withdrawn in favour of electric vehicles.

The island is served by Şehir Hatları ferries from Kabataş and Eminönü on the European side of İstanbul and Kadıköy and Bostancı on the Asian side.