The phrase "A City within a City' is a match for ----

The World Trade Center complex housed more than 430 companies that were engaged in various commercial activities. On a typical weekday, an estimated 50,000 people worked in the complex and another 140,000 passed through as visitors. The complex hosted 13,400,000 square feet (1,240,000 m2) of office space, and was so large that it had its own zip code: 10048. The towers offered expansive views from the observation deck atop the South Tower and the Windows on the World restaurant on top of the North Tower. For this reason, it is called "A City within a City'.