island of Delos, and the Medieval City of Rhodes. Greece is one of the most visited countries in Europe and the world with over 33 million visitors in 2018, and the tourism industry around a quarter of Greece's Gross Domestic Product. The islands of Santorini, Crete, Lesbos, Delos, and Mykonos are common tourist destinations. An estimated 2 million tourists visit Santorini annually. However, concerns relating to overtourism have arisen in recent years, such as issues of inadequate infrastructure and overcrowding. Alongside Greece, Turkey has also been successful in developing resort areas and attracting large number of tourists, contributing to tourism in Turkey. The phrase "Blue Cruise" refers to recreational voyages along the Turkish Riviera, including across the Aegean. The ancient city of Troy, a World Heritage Site, is on the Turkish coast of the Aegean. Greece and Turkey both take part in the Blue Flag beach certification programme of the Foundation for Environmental Education. The certification is awarded for beaches and marinas meeting strict quality standards including environmental protection, water quality, safety and services criteria. As of 2015, the Blue Flag has been awarded to 395 beaches and 9 marinas in Greece. Southern Aegean beaches on the Turkish coast include Muğla, with 102 beaches awarded with the blue flag, along with İzmir and Aydın, who have 49 and 30 beaches awarded respectively. See also Exclusive economic zone of Greece Geography of Turkey List of Greek place names References External links Seas of Greece Seas of Turkey Marginal seas of the Mediterranean European seas Seas of Asia Geography of Southern Europe Geography of Western Asia Landforms of Çanakkale Province Landforms of Muğla Province Landforms of İzmir Province Landforms of Balıkesir Province Landforms of Edirne Province Landforms of Aydın Province