Part 4/11:

While ancient echoes resonate through Beijing’s underground, a more recent chapter unfolds in the tunnels constructed during the Cold War, known as the Beijing Underground City. Built between the late 1960s and 1970s as a protective measure against potential nuclear conflict, this expansive network was meant to shelter the city's residents. Dubbed the "Underground Great Wall," it was designed to accommodate the entirety of Beijing’s population, now over 6 million.