3. Nan Madol (Micronesia)
Nan Madol, located off the eastern shore of Pohnpei Island in Micronesia, is an ancient city comprising over 90 artificial islets connected by a network of canals. Constructed between the 8th and 17th centuries, the site served as the ceremonial and political center of the Saudeleur dynasty. The islets are built using massive columnar basalt stones, some weighing up to 50 tons, transported from quarries elsewhere on the island. These stones were laid using a distinctive ‘header-stretcher technique’ to form walls and structures. The construction methods and the purpose of the site remain subjects of ongoing research and debate. (whc.unesco.org)
