3.5 km southwest of Kos is the most renowned and long-lasting monument on Kos,
the Asklepion.During antiquity buildings such as the Asklepion were sacred
therapeutic centres and this specific one is considered to be one of the most
important since it remained in operation for many centuries. Building work on it
began during the 4th century BC although finds from the Mycenean and Geometric
periods have been found at the same location. It is laid out over three
terraces. On the first terrace are the Propylea, the ruins of baths, stoas and
buildings erected by Vespasian.
On the second terrace is the ancient temple of Asclepius (3rd century BC), the altar of Asclepius or Apollo Cyparissus (4th century AD), the remains of another temple of Apollo (3rd century AD) with seven columns re-erected. Lastly on the third terrace are the ruins of a major temple of Asclepius (2nd century BC) and the traces of a Hellenistic stoa.
At Pyli lies the so-called Harmylos Grave, a total of 12 dome-structured tombs. At Kefalos are the ruins of a Hellenistic theatre at the location known as Palatia, some 3 km south of the village.
In Kos town exactly at the entrance to the port is the Knight's Castle or Nerantzias Castle as it was once known, built atop the ruins of an ancient fortress. Construction was begun by the Knights of St. John in the 14th century but took a considerable time to complete due to delays caused by Turkish raids. The castle has a double curtain wall and until the beginning of the 20th century was a separate island since it was cut off from dry land by a moat filled with seawater. Today this is covered over by Finikon Ave.
The castle was linked to dry land at the location of Hippocrates' Plane Tree by a bridge which has been preserved to this day. It is located above Finikon Ave.
At Antimachia, 4.5 km southeast of the village is an exceptionally well-preserved medieval fortress. In Pyli the ruins of a Byzantine fortress stand atop a hill from where there is a wonderful view of nearby islands. There are similar ruins on a hilltop at Kefalos.
Monasteries and Churches :
In what is today the ruined village of Paleo Pyli, atop a hill to the southeast of the village are three churches set among exceptional surroundings, those of Aghios Antonios, the Archangels (Taxiarches) and Panaghia Ipapandi, which in the past was the Monastery Kastrianon founded by Blessed Christodoulos.
Of these three churches Ipapandi is of greatest interest since remains of wall paintings from the 14th century have survived as well as a carved wooden iconostasis and ancient columns, which, in all likelihood, were brought here from the nearby temple of Demeter.
At Mastihari there are ruins of a Paleo-Christian Basilica from the 5th century with mosaics covering an area of 400 m2 in an excellent state of repair.
At Antimachia inside the medieval fortress are two post-Byzantine churches.
At Asfendiou is the Asomaton Taxiarchon Church dating from the 11th century with an ornate iconostasis as well as a Paleo-Christian basilica dedicated to St. Paul. This lies just outside the village. Atop Mt. Dikeos, known as Oromedon in antiquity, lies the Church of Christ with its breathtaking view.
At Lagoudi is the picturesque church of Aghios Ioannis Theologos built among the rocks.
At Kardamena is a Paleo-Christian basilica dedicated to Aghia Theotita. Lastly, there are several remarkable churches in the Kefalos area including the remains of a Paleo-Christian basilica of St. Stephen with a mosaic floor and columns. It dates to the 6th century. Other churches worthy of a visit are Panaghia Palatiani at Palatia, Panaghia Ziniotissa, Aghios Mamas, Aghios Theologos and Aghios Ioannis, all with exceptional views of the surrounding areas and the sea.
The proximity of the active volcano on Nissyros as well as the particular geological and tectonic structure of the wider area favour the presence of subsurface spa spring aquifers on Kos. In the area known as Embros Thermes around 4 km west of Aghios Fokas Cape is a spring set amid wild landscape renowned for its high water temperatures (40-47°C) and high sodium, potassium, magnesium, calcium, and chlorine and sulphur anion concentrations.
Another spring abandoned today is in the Piso Thermes or Aghia Irini area east of Kardamena inside a cave. This is accessible from the sea only. There are another two springs, one hypothermal and one with cold mineral water, in the areas of the Asklepion and Kokkinonero respectively.
There are few caves on Kos with the main one being Siderotrypa on Mt. Dikeos and those in the locations known as Schistres, Lagoudi and Zias while there is also one at Aspri Petra near Kefalos.