These rare underground caves were formed when the surface lava from the now extinct nearby volcanoes cooled and solidified, while the hotter underground lava continued to flow, leaving a hollow space.
The lava tubes are almost halfway between Ho Chi Minh City and Dalat. First locate the teak forest on Hwy 20 between the Km 120 and Km 124 markers. The children who live close by can show you the entrance. Take a torch (flashlight) and go with a guide.