Chom Ong Cave is a cave system located in Oudomxay Province, in the north of Laos. Featuring a length of more of 16 km, it ranks now as the longest cave in Northern Laos and is one of the top 10 in all Laos. Naming The villagers of Ban Chom Ong call the cave „Tam Chia“ (Lao: Bat Cave), as they traditionally hunt bats in the cave as food and exploit guano, which can be used as fertilizer, explosive agent or gunpowder. For better distinction from other caves in Laos which are called "Tham Chia". Scientist groups choose to call it by the village name, "Chom Ong". Location and Infrastructure The cave is located about 45 km from Muang Xay, capital of Oudomxay Province, at the border of Xay District with Nam Or District. It is accessible starting from the nearby village Ban Chom Ong, which is inhabited by people of the ethnic group Khmu. The road leading from Muang Xay to Ban Chom Ong is a hilly dirt road, which makes access to the village difficult during the rainy season. During the dry season it is possible to reach the village by motorcycle or car in about two and a half hours. Starting from the village, the cave is accessible by a 45-minute walk. Geology The system stretches along a 4 km long mountain ridge and has a parallel running and interconnecting fossil and river passage. In two explorations (2009 and 2010) it was explored to a length of 16.4 km (preliminary) with several wide open side passages remaining. The typical passage dimension is 20–25 m width and 20–30 m height. Two huge overlaying halls mark the connection of river and fossil passage with each 100 m length, 30 m width and ceiling heights of 30–50 m. The cave is a trough cave and could be entered with exploration equipment near the stream inlet in the north and left at the outflow in the south. The full traverse would take about 5 hours with additional 1 and 3 hours respectively return walking time to Chom Ong village. The cave was pushed at the last day in a 15-hour trip to its current length. The upper level of the cave leads to several about 15 meter high "balconies", from where it is possible to look down to a lower level, where the Nam Kaang river flows. Chom Ong Cave features