As modern man advanced into the nuclear age, he ironically retreated deeper into caves at the same time.
Underground bunkers and tunnels have long been a haven for bombs dropped from the sky. As the bombs became more powerful, the tunnels were dug deeper into the earth and mountainsides to absorb the impact.
During the 1970s, China dug very deep and very far to prepare for Soviet or American attacks. In all, the Chinese built 62 miles of tunnels over a ten year period to serve as bomb shelters in case foreign bombers ever took flight over Red China.
Thankfully this never happened and in 2000 the Chinese government opened the tunnels up for tourism. Only a small portion can be seen but according to an informative travelogue on TravelChinaGuide.com, it is well worth a visit.
Guides claim that the overall network worms its way throughout the city, connecting government palaces with railway stations the airport and other strategic centers. The tunnels are damp, cold and best visited on a hot Beijing day. And, they are well off the beaten path. Few, if any guidebooks mention their existence, but directions can be found here.