Prickly Pear

Opuntia ficus-indica. Φραγκόσυκο (Fragósiko) in Greek. Both cultivated (fence!) and wild around the Mediterranian Sea. You can eat the fruit,  I read in my  Swedish flowerbook: "Blommor och träd vid Medelhavet" by Tore Hylander. I don't think you can find this book in English, but of course there are similar ones. This cactus is also planted at volcanic lands to decompose lava and to create new soil - interesting!