Located within the Phu Hin Boun national park, this is the most spectacular cave in the Thakhek region. For 7.5km, an underground river, Nam Hin Boun, runs through it, along whose winding course visitors can travel by motorised boat. The size of some its rooms (up to 50m in height), and the play of light and shade provided by the powerful lamp torches on its columns, stalactites and stalagmites, make this an unforgettable experience for visitors.