Chairman Mao's underground city

Apparently, there exists beneath Beijing a series of secret chambers and passageways, the likes of which rivals the Paris catacombs. From Pmgtg.com:

In 1969, Chairman Mao commanded the construction of a second Beijing beneath the surface of the original city, designed to accommodate all six million of its then inhabitants so that if nuclear war did kick off, folk would still have somewhere to hang out and play Mah Jong while the rest of us burnt to death in a shower of atomic rain. War never came, but the city is still there.

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