LAOS // Concealed within the dramatic karst landscapes of Vieng Xai is a complex system of caves that, at one time, sheltered more than 20,000 soldiers and civilians. Open to the public since 2007, the fascinating caves were home to the Pathet Lao communist leadership during the so-called 'Secret War' and US bombing campaign of 1964-73. Basic bunkers were transformed over time into an underground city of hospitals, markets, a printing room, theatre and even a metalwork factory. Fittingly, it takes some effort to get here, but it's worth it.