Lying 30 kilometres east of Sam Neua close to the Vietnam border, Vieng Xai is one of the hardest to reach corners of Laos and is also home to one of the country’s most important historic sites, the Vieng Xai caves. A tiny town set on a plain guarded by hulking limestone karst, Vieng Xai’s peaceful landscape and sleepy demeanour belies its powerful role during the Secret War as the command centre of the Pathet Lao. Those karst contain hundreds of caves and from 1964 to 1973, as bombs rained down, 20,000 soldiers and civilians survived in a hidden city. The caves are the main reason for visiting Hua Phan Province. The principal caves are open to the public, only accessible via a three hour tour paired with an excellent 18-point audio guide. The tour includes the leadership quarters, barracks, meeting room, emergency safe rooms, cooking areas, artillery caves and a giant theatre. Meanwhile, the audio paints a picture of what it was like living in the damp, dark underground, the narration layered with survivors’ stories. Vieng Xai is a truly remarkable part of the country and makes a compelling case to journey to this remote frontier.