Whether man-made or reclaimed from nature, islands near cities hold a certain appeal for urban areas looking to add green public space amid increasing density: New York’s Governors Island, for example, or Northerly Island Park in Chicago. In Seoul, one of the most population-dense cities in the world, the opportunity to create a satellite park for the capital came in the form of land that, until the 1970s, had been attached to the mainland and engineered to serve as a beach. Originally part of the Han River’s northern bank, the beach became partly submerged in the 1970s—as the river expanded and the construction of protective dikes led to changing currents—to become 30-acre Nodeul Island.