As usually happens in tropical karst areas, many caves are the underground domain of rivers that, throughout their course meet calcareous ridges, and at the foot of large blind valleys big portals open up and rivers suddenly disappear to re-emerge somewhere else.

In the region south of Kalaw there are many caves of this kind but we had the opportunity of exploring them only partially during the 2005 expedition. One of them is formed by a large tunnel connecting two adjacent valleys. Evident traces of transit found in the cave prove that it was used as a route of communication in the past. We explored another cave for a kilometre; it was rich in water fauna, such as giant prawns and blind fish.
The largest ponor we discovered is located at a three hour walk from Pinh-ton, a remote mountain village, 80 km south of Kalaw. The river plunges in a 50 m waterfall, that was impossible to descend due to the huge amount of water, and continues its flow in a vast canyon that carries on in the dark. The river re-emerges from the springs of Namun, around 7km away.

It is a wonderful place that can be reached in 3 hours by boat sailing up the river. Here, at the foot of a limestone cliff, a small cave appears as an underground lake in which we hear the sound of a waterfall. What is between ponors and natural springs is still unknown; for sure it is a vast underground system of water tunnels yet to be explored.