The Haew Suwat Waterfall was probably the most popular waterfall in Khao Yai National Park. We felt this was the case because of its ease of access, its vicinity to a major campsite, and the heaps of people that were both around the falls as well as the short trail to get to its bottom. We thought Namtok Haew Narok was busy, but this waterfall put it on another level.
We made our visit during the Dry Season so the 15m or so waterfall was split into a pair of parallel segments. The dual plumes dove right into a boulder-fringed dark plunge pool at its base. We saw there were some people who managed to swim then scramble their way to what appeared to be a cave-like alcove almost behind the waterfall.
In any case, I'd imagine in the Wet Season, the falls would take on a thicker appearance, but it might lack the character that you might observe in the falls from looking at the photo at the top of this page. In other words, this waterfall might be one of those cases where "less is more".
Even though we took a real short 15-minute walk to the bouldery edge of the fairly wide plunge pool at its base, there was a separate, short trail that went to the top of the waterfall. We saw numerous people who were chilling out from the top of the falls, which provided us with a sense of scale as to the height of the falls.
During the short walk down to the base, we also noticed there was also an upper lookout platform offering up a a different perspective of the falls (albeit with a partially obstructed view). All in all, we spent about 45 minutes on our visit, which consisted of just the walk to the base and the overlooks along the way. However, we didn't do the other trail leading to the brink of the falls.
Directions: Since we were escorted, we can't give exact directions. However, we can say that it took us between 45-50 minutes of driving from the Haew Suwat Waterfall to the accommodations in town near the Khao Yai National Park entrance.
Khao Yai was about 3 hours northeast of Bangkok or 2 hours east of Ayutthaya.