Diagram by Greece Trips. Free to reuse with credit - CC BY 4.0.
Its walls incorporate ancient stone, columns and inscriptions taken from earlier buildings on the island, which is visible in the masonry once you know to look.
Check access before you go
The July 2017 earthquake damaged the castle, and access has varied in the years since, with sections closed and reopened at different times.
That is not a reason to skip Kos Town; it is a reason to take the current position from the Hellenic Ministry of Culture or the local ephorate rather than from a travel page, this one included, before planning a morning around going inside. Our things to do in Kos page carries the same caution.
What you see from outside
Quite a lot, which is the useful part if the interior is closed. The castle is separated from the town by a bridge over what was once a moat, and the walls, bastions and the harbour front can be walked around at ground level.
Beside the bridge stands the plane tree traditionally associated with Hippocrates teaching beneath it. The age claims that circulate are legend wrapped around a genuinely old tree, and it is more enjoyable treated that way.
Where it fits in the town
Kos Town keeps its ruins in the street rather than behind one gate: the ancient agora sits behind the harbour, the western archaeological zone holds mosaic floors and colonnaded streets, and the Roman odeon and the Casa Romana are a short walk inland.
The castle is the top layer of that stack, and the walk between them all is short and flat, which on this island is the recurring theme.
Last checked August 2026. Access has varied since the 2017 earthquake and hours change - see our editorial policy.
Common questions
Who built Neratzia Castle on Kos?
The Knights of St John, as part of their network of fortifications across the Dodecanese, reusing ancient stone from earlier buildings on the island.
Can you go inside Neratzia Castle?
Access has varied since the 2017 earthquake damaged parts of the structure. Check the current position with the Ministry of Culture or locally before you go.
Where is Neratzia Castle?
On the harbour mouth at Kos Town, reached by a bridge over the former moat beside the plane tree.
Is the plane tree really Hippocrates’ tree?
It is an old tree with a strong tradition attached. The specific age claims are legend rather than established fact.
What else is near the castle?
The ancient agora behind the harbour, the western archaeological zone with its mosaics, the Roman odeon and the Casa Romana, all within a short flat walk.
Next
Read things to do in Kos, the Asklepion, or where to stay in Kos.