Asia, Lao PDR, Khammuan Province, Hin Nam No National Park, 30.11.2011. A view of the downstream entrance of the Xe Bang Fai cave. The Xe Bang Fai river runs through this limestone cave for 12 km, making it one of the longest river caves in the world. © 2011 GIZ/Lucas Wahl/Kollektiv25/Agentur Focus[/caption]