This amazing castle is located next to the port of Kos and it is also called the "Mandarin" castle because Kos, at one point, was full of manadrin and lemon trees. You do need to pay an entrance fee to go inside, which is about 10 euros, and it will take your about 1 hour to explore. It is quite hot during the summer, so it is best to go in the morning or late afternoon with your water and bottle of sunscreen. There are very nice views of the town, the sea, and harbor. This castle, as well as the Tree of Hippocrates (see my other story), are two of the most well known sites of the island, with descriptions and pamplhetes available in multiple languages.