Chom Ong, Cave system in Oudomxay Province, Laos

Chom Ong is a cave system in Oudomxay Province, northern Laos, with a surveyed length of 16.4 km along a 4 km mountain ridge. It has parallel fossil and river passages linked by two huge overlaying halls, each 100 m long, 30 m wide and 30–50 m high. The Nam Kaang river flows through the lower level, and balconies about 15 m above it overlook the water.

Scientific exploration of this cave system began in 2009 when international research teams first mapped and measured the passages. These investigations established it as one of the longest cave systems in Northern Laos and brought attention to the region's geology.

The Khmu community in Ban Chom Ong village traditionally hunted bats here and collected guano as a resource. The name 'Tam Chia' refers to the bats that inhabit the cave and shaped the daily practices of local people.

The cave entrance lies about 45 kilometers from Muang Xay, accessible via a dirt road to Ban Chom Ong village. From the village, plan for a 45-minute walk to reach the main entrance.

The Khmu name Chom Ong means "beehive", pointing to beekeeping as a traditional village trade. Villagers long called the cave Tam Chia, or bat cave, and hunted bats there for food while collecting guano used as fertiliser, explosive agent or gunpowder.