Sixteen kilometres south of Sekong, and well-signed off Rte 11, is this wide, beautiful 5m-high waterfall where you can swim in the pool atop the falls. At the time of our visit, the concession that had run the place for many years, including shacks to stay in at the top of the falls, had had its licence revoked, and there was no one there to collect entry fees. It is still a nice place to wander around, though.
If and when new management takes over, the picture (including entry fees) will certainly change.