Between the resorts of Argostoli and Lassi are the villages of Peratata and Travliata and, above them, the remarkably well preserved Venetian Castle of St George (Agios Giorgios) with coats of arms decorating the massive bastions, one of which conceals a secret tunnel which ran to a lagoon in Argostoli.
The original castle was Byzantine and probably built in the 12th century. The external walls that survive today were constructed by the Venetians in 1504. You can still see cannon placements, observation posts and the remains of a bridge. The castle is usually open in the he summer though sometimes closed for restoration work. Check in the village first.
Beneath the castle walls is the Kastro with remains of houses and panoramic views over the island. There are the remains of churches and a welcome cafe, bar and restaurant. Peratata itself is also home to the gorgeous monastery of Agios Andreas filled with 17th century frescoes and its prize relic, the sole of St Andrew's foot. It also has a notable icon collection.
The road leads to the village of Lakithra, where Lord Byron wrote his epic Don Juan. The view over the plain below are astonishing and on a clear day you can even see the island of Zakynthos.