The Pearl River estuary in South China separates cities on either side, hindering easy access. The Shenzhen-Zhongshan Link, a project of bridges, islands, and a tunnel, has changed that. Completed in seven years and setting 10 world records, its underwater tunnel is as large as 32 aircraft carriers side by side. Now, Shenzhen, Zhongshan, and all 11 cities in the Greater Bay Area are more closely connected than ever.