The beautiful limestone-karst countryside of the remote Houaphanh Province in Laos’ north east is picture postcard perfect. This excellent start- or end-point of the Northern Heritage Route, situated near the Vietnamese border, is charming idyll of peace. But for nine long years it hid a secret city while death rained from the air. Within those limestone walls, an interconnected series of more than 400 caves and tunnels not only provided shelter for 23 000 people from the incessant bombs dropped by the Americans in the ’Secret War’, but also bakeries and schools and a hospital, printing press, radio station, theatre and – most significantly – offices for the fledgeling Pathet Lao leadership – the seven-man politburo that would go on, post-war, to become the communist leadership of the Lao People’s Democratic Republic.

Though access to foreigners was previously forbidden, tourists are welcomed these days, and an excellent 18-point audio tour provides real insight into the lives and workings of this hidden wartime city, with the first-hand accounts particularly moving. “A moving, balanced and uniquely fascinating glimpse of how people struggled on through the war years,” is how Lonely Planet describes it. “Compared to anything else you’re likely to encounter in Laos, the sheer professionalism is mind-boggling.”

Wanderlust magazine published a great article about a visit to the caves, and some of the history.