Just in front of the main gate of the Knights' Castle, there is an imposing huge plane tree. This perennial tree, «the plane tree of Hippocrates» as the locals call it, is of a perimeter of more than 10 meters.
The early Christian Basilicas at the beach of Agios Stefanos, within Kefalos bay, are dated in the 5th or 6th century. There is the southern and the northern one.
At the entrance of the port of Kos it is situated the so-called «Kastro tis Neratzias». In the 14th century the Knights of the Order of St. John who dominated the island, decided to construct the castle to assure the defense of the town.
A flourishing Jewish community existed in Kos, since the period of the Second Temple. The Knights of St. John dispersed the Jewish community until they came back in 1522.
Situated at small distance from the Agora and the port of the ancient city of Kos, the Altar of Dionysus is a good example of a Π-shaped altar of the Hellenistic period. The part preserved is dated in the 2nd century b.C.
The area of the archaeological site of ancient agora is successive to the port of Kos and is situated at the eastern end of the island. Several public buildings and sanctuaries were constructed at the area both of the Agora and of the ancient port.
The Archaeological Museum of Kos is distinguished by three entrances topped by arches. Several sculpture are displayed in three rooms surrounding the atrium, which is decorated with a mosaic presenting the arrival of Asklepeus at Kos.
Asklepieion is the most well known ancient monument of the island. The monument was built on a hillside overlooking the area, with an excellent view of the sea below and of the opposite coasts of Asia Minor.