Kos lays at the mouth of the Turkish Gulf of Kerme, which cuts deep into the coast of Asia Minor. It was separated from the Bodrum Peninsula by the collapse of a rift valley in the Pliocene period, which explains the range of limestone hills, rising to 846 m in Mount Dikaios, that runs along the island for almost its entire length.
It is the largest island in the Dodecanese after Rhodes and, unlike most other Aegean islands, Kos has a population that is increasing in numbers.

Kos has been well populated since Neolithic times. About 700 BC, together with the five other cities of the Hexapolis (Knidos, Lalysos, Lindos, Halikarnassos and Kamiros), Kos was an outpost of the Dorian League. The island was celebrated for the oldest cult site of the healing god Asklepios and for a medical school of which the most famous representative was Hippokrates (5th century BC).

Kos Port is located in a large shallow bay, the west side inside the harbour is for charter yachts only. The east side of the port boasts the Castle of the Knights (1450-80) with a road full of matching palm trees. Kos town is full of bougainvillea, jasmine and exotic whiffs of the middle east.