Tham Kong Lo

Tham Kong Lo, also spelled Konglor, is a river cave that you pass through by boat. In the karst mountains of Phu Hin Bun National Park, in Laos's Khammouane Province, the Nam Hin Bun river runs straight into a limestone massif and emerges on the other side about 7.5 km later, making this one of the longest river passages through a cave anywhere. Inside, the tunnel reaches up to about 90 metres wide and 100 metres high, and in the wet season the river carries a great volume of water; the whole cave system has been surveyed to over 12 km.

Visitors make the crossing by boat along the underground river, and on the way they see stalactites and other limestone formations in the huge passage. The cave has been described as one of the geological wonders of Southeast Asia, and a pool inside that glows a vivid emerald green is held sacred by local people. In recent years villagers have set up stalls near the entrance to serve the growing number of travellers.

For the people of the region the tunnel was once a frightening barrier rather than a road. The first known crossing by rowing boat was made in 1920 by five volunteers with torches, and even after that, villagers travelling between Kong Lo and the Natane valley on the far side preferred a hard six- or seven-hour walk over five mountain passes. Today the cave links the two worlds, and tourism has become, alongside rice and tobacco, one of the main sources of income for the remote valley, where some villages are almost self-sufficient during the monsoon.

Getting there

The cave is at Ban Kong Lo village, about 130 km by road north of Thakhek, the provincial capital, which lies about 60 km away as the crow flies. The nearest international airport in Laos is Wattay in Vientiane (VTE), about 233 km away; across the Mekong, Nakhon Phanom in Thailand (KOP) is closer on the map but requires a border crossing. The crossing is made by boat; water levels change sharply between the dry season and the monsoon.