I planned to cycle into Khao Yai this weekend just gone but didn't have the energy after cycling 50km from the other side of Nakhon Nayok. The sun and heat is brutal at this time of year, I should have taken that into account and cycled early morning or late evening. I resigned to staying around Wang Bon area before heading back to Bangkok the next day.
Than Rattana WF on first glance is easily written off as another Thai 'waterfall' that is actually more of a stream with a few small drops of water. That's what I did when I first checked it out a few years ago. It's a 20-metre walk down some steps from the main road, and there is only significant water in rainy season. It doesn't even have an English sign or a carpark but this understated appearance is deceptive because there is a lot going on downstream if you are prepared to adventure a little.
When Googling the name you are presented with a bunch of images of people abseiling down various levels of a waterfall, which doesn't compute as you stand there looking at a 1-metre cascade of water. Unless you come in peak rainy season or after heavy rain, the riverbed should be wide enough to wander comfortably downstream 500m where you will find the first proper waterfall and things start to slot into place. To my knowledge there is no trail for this first part; you have to go via the riverbed. This makes sense if we consider that organised groups are abseiling down the waterfalls - they are already drenched (or about to be drenched) and are probably walking down the riverbed for the most part too.
On my visit there was only a trickle of water and it was much easier for me to scramble down some of these drops than it would be if there was a stronger flow - in that case you might have to cut into the forest occasionally before rejoining the riverbed. I swam across one of the pools rather than enter the forest and it was still deep enough for me not to be able to stand. Looking at photos of the abseiling groups, it seems they are choosing times of year to do it when there is water, but not too much water that it might become too slippery and dangerous. I think late December, January, possibly into February would be ideal, and maybe late May into June.
Another 500m or so downstream and you get to the top of a much larger drop, and there isn't any obvious way down from either side of the river bank. This water has cut out a really impressive hollow in the mountain which reminds me of Haew Narok. I can imagine in rainy season it would fill up like a bath.
You can scramble down using vines as ropes but if you approach it from the top as I did it won't be obvious and I only figured out that route on the way back up on the return journey, after I had gone back and found a trail (sometimes clear, sometimes not) through the forest. When I was trying to find the way down I got my first view over Wang Bon Reservoir and the fringes of Khao Yai.
Immediately after that drop there is another, which is more easily traversed, and then after that it is quite flat until you get to Wang Bon reservoir.
I noticed a few of the climbing fixings at various places on the route.
When the river joins the reservoir there is a final waterfall which you can see on these TAT promotional images:
This is the same waterfall mentioned at the start of this thread which is often kayaked to. It's called Yai Phao WF.
This is definitely a river system I'd like to check out properly when there is some water! For a hardcore adventure you could start at Wang Bon, walk around the edge of the reservoir (or swim) to the first waterfall, walk all the way up the riverbed to the road, walk 2km down the road and cut back through the forest to Wang Bon using the trail mentioned at the start of the thread. Remember this is all national park so staff would probably be interested if they saw you swimming across the lake or walking on the Khao Yai road without a vehicle. To confirm it is possible to go up or down without abseiling and without forging much of a path through the forest, but that one section at the highest drop where you have to use vines to pull yourself up is a bit technical/sketchy, and you can't see the route properly if lowering yourself down because it's almost vertical in parts. I noticed some hoof prints in the sand next to the river near the road, probably deer, and some small elephant prints again in the sand but this time nearer the reservoir.
Here is the TAT description of the abseiling walk, the website is not coded well and the maximum drop height of 70m is at least 50% exaggerated:
adventure.tourismthailand.org/eng/rock-c.../namtok-than-rattana
As of March 2022 Wang Bon kayaking and camping area is shut but still staffed, the HQ area looks dilapidated and the barrier is often closed. It's been that way since covid. People seem to be allowed to walk in or scooter around the barrier, and the actual dam viewpoint is before the barrier anyway. On weekends the viewpoint is full of bikes and cars playing loud music from sunset until late.