The modern town lies on a flat plain encircling spacious Mandraki Harbor and is a pleasant assemblage of low-lying buildings and shady lanes, with a skyline pierced by minarets and palm trees. Its main waterfront, though attractive, doesn't have the best of reputations thanks to the rows of harborside bars that churn out customers deep into the small hours. Yet the area's history dates to long before a time when it had to rely on its tourist crutch, and is easily seen, in scattered ancient ruins, remnants of old city defences draped in creepers, and an imposing medieval castle.
Platanou Square is a good place to start. It was here that Hippocrates (460–370 BC), the father of modern medicine, is supposed to have taught, in the shade of a plane tree that grows on one side. Many say this is merely legend; not least because the tree that now stands here, propped up by spidery scaffolding, is just five centuries old. Surrounding this are relics of the island's Turkish past (1523–1912), including a loggia that is actually a mosque built in 1786, and showpiece buildings erected during Fascist Italian rule (1912–43), known as the Foro Italico area. Going back further, this square was once the center of a fortified medieval city, connected to the grand castle, built by the crusading Knights of St. John, that lies across the road. Sadly, this is no longer open to the public after an earthquake in 2017 rendered it unstable, but you can still wander the city's old vine-clad fortified walls east of the harbor.
Relics of Kos's Hellenistic and Roman past can be explored everywhere, not least in the remains of an old Roman home that sits on the outskirts of town. An earthquake in 1933 allowed for proper excavations of the town center, and much of what they found is now on show in the main museum.