Hin Nam No National Protected Area, Protected area in Khammouane Province, Laos.

Hin Nam No is a national park in Boualapha District, Khammouane Province, covering 94,000 hectares, of which 77.5% is forest. Its karst formations lie between the Khammuan limestone belt and the Annamite Range, with limestone escarpments and caves including the Xe Bang Fai River Cave, whose passages reach about 120 metres high and 200 metres wide.

Hin Namno was created by prime ministerial decree in January 2020 and is managed by the Ministry of Agriculture and Forestry. In early 2021 it was nominated for the IUCN Green List of Protected and Conserved Areas, and in 2025 it joined the World Heritage List as an extension of Vietnam's Phong Nha-Kẻ Bàng National Park.

The Xe Bang Fai River flows underground through the karst landscape and disappears below the surface at several points, where fishermen traditionally use boats to catch fish near certain cave entrances. Surrounding villages have relied for centuries on rice farming and the collection of forest products such as bamboo, resin, and wild honey.

Visitors must arrange permits and local guides through the administration office in Boualapha District before entering. The best time to visit is between November and March, when trails are drier and cave access is easier.

The Xe Bang Fai cave passage extends over 7 kilometers (4.3 miles) and ranks among the longest navigable underground rivers on Earth. During the dry season, boaters can travel deep into the chamber and see stalactites hanging directly above the water.