This is "The Jewel in Tad Kwan's Crown", Nam Tog Tad Kwan (Nam=Water, Tog=Fall) is by far the best waterfall in Chiang Rai province. The swimming hole at the base of the waterfall is about 80m x 25m and in places 4m deep. It is never visited by organised tours since to get to it by road is extremely difficult involving 25km trip off the highway down a road which ends at the waterfall. It's a popular destination for local folk who often hold their weddings here for good luck and for children in the 'hot season' school holidays who enjoy swimming here.
We have our own special way of visiting this waterfall. We have a fleet of 4 wheel 'drive-yourself' buggies with roll cages, seat belts and automatic transmission. Each buggy seats 2 people, a driver and a passenger and our journey there is entirely off-road.
The journey to the waterfall and back takes up the afternoon session (very occasionally, the morning session), about half of it is spent in a buggy driving through the countryside.