Dominating the harbor, the Castle of the Knights stands in and atop a long line of fortresses defending Kos since ancient times. What you see today was constructed by the Knights of St. John in the 15th century and fell to the Turks in 1522. Satisfying your curiosity is perhaps the only compelling reason to pay the 4€ admission fee. The castle is a hollow shell, with nothing of interest inside that you can't imagine from the outside, except when it serves as a venue for concerts. Best to stand back and admire from a distance this massive reminder of the vigilance that has been a part of life in Kos from prehistory to the present.

At the edge of town, at the intersection of Vas. Pavlou and E. Grigoriou, stands the Casa Romana (tel. 22420/23-234), a Roman villa that straddles what appears to have been an earlier Hellenistic residence. The largest Roman villa in Greece (with 37 rooms), it was actually built and rebuilt over the centuries, and what you see today is the villa of the 3rd century A.D., one with lavish mosaics, marble paving, and fountains. It was closed to the public in 2005 for major restoration but reopened in 2009 (and there has been talk of using the villa's upper story as a museum for the villa's finds, now in Kos town's Archeological Museum). The villa is open Tuesday through Sunday from 8:30am to 3pm and costs 3€ for adults. Nearby, to the east and west of the Casa Romana, are a number of interesting open sites, comprising what is, in effect, a small archaeological park. Entrance is free. To the east lie the remains of a Hellenistic temple and the Altar of Dionysos, and to the west and south a number of impressive excavations and remains, the jewel of which is the Roman Odeon, with 18 intact levels of seats. The other extensive area of ruins is in the agora of the ancient town, just in from Akti Miaouli. Kos town is strewn with archaeological sites, opening like fissures and interrupting the flow of pedestrian traffic. Rarely is anything identified for passersby, so they seem like mere barriers or building sites.

The rich architectural tradition of Kos did not cease with the eclipse of antiquity -- Kos is adorned with a surprising number of striking and significant structures, sacred and secular, enfolded unselfconsciously into the modern town. While you're strolling about town, note the sculptures by Alexandros Alwyn, in the Garden of Hippocrates, opposite Dolphins Square, down along the Old Harbor. An English painter and sculptor with something of an international reputation, Alwyn long maintained a studio in the village of Evangelistra, on Kos.

The Oldest Tree in Europe? -- From the Kos Museum, you might want to walk across to the Municipal Fruit Market, and then have a picnic at the foot of the oldest tree in Europe, only a short walk toward the harbor, at the entrance bridge to the castle. The bizarre-looking tree standing with extensive support is said to be the Tree of Hippocrates, where he once instructed his students in the arts of empirical medicine and its attending moral responsibilities. Botanists may not endorse this claim, but why not enjoy the legend!

Note: This information was accurate when it was published, but can change without notice. Please be sure to confirm all rates and details directly with the companies in question before planning your trip.