There is a wonderful booklet available, “Kythira on foot’, with 32 walks all around the island. They are mostly circular walks, with the same departure and arrival point, so you can just park your car and start hiking. The booklet is available in English but also in Italian, French, Greek and Dutch.
The price is € 12,50. It is on sale at the bookshop Βιβλιοχαρτοπολειο in Potamos (opposite of the supermarkt).