This place exists in Essex England. I've visited it twice when living in the UK. There are signs along the way advertising it. Its at Kelvedon. Known as the Secret Bunker or the Kelvedon Hatch. In fact it is not really secret anymore. It was built during the Cold War. There is an inconspicuous farm house but underneath is a huge underground network designed to protect the English govt should there be the hint of nuclear war. It is very interesting. But I did find the signs leading to it amusing.