Photo taken on May 3, 2019 shows the scenery of Delos, Greece. Delos, once a booming trading center in the middle of the Aegean Sea near Mykonos, is a UNESCO world heritage with a history of 5,000 years. Delos is revered in Greek mythology as the sacred birthplace of twins Apollo, god of light, and Artemis, goddess of the hunt. (Xinhua/Li Xiaopeng)