10 biggest underground systems in the world

10 biggest underground systems in the world

10 biggest underground systems in the world 10. Chongqing Rail Transittotal length: 370 kmlocation: Chongqing (China)year of discovery: 2005last expansion: 2021number of passengers in 2020: 839,750,000 9. Nanjing Metrototal length: 378 kmlocation: Nanjing (China)year...