Pretty impressive when everyone Digs!
Beijing has a 20,000-acre secret underground city, Dìxià Chéng, that was built during the Cold War by 300,000 people digging by hand
http://www.spiritualvigor.com/2018/11/beijing-has-20000-acre-secret.html?m=1
Beijing has a 20,000-acre secret underground city, Dìxià Chéng, that was built during the Cold War by 300,000 people digging by hand
http://www.spiritualvigor.com/2018/11/beijing-has-20000-acre-secret.html?m=1