Khao Yai is one of the two WHS that can be reached from Bangkok within a day trip (the other one is Ayutthaya). I hired a car with a driver for the day. From central Bangkok to the visitors center in the park it takes about 3 hours (largely spent in Bangkok's traffic jams). When you start seeing mountains and forests instead of cars and shops, you're nearly there. We entered the park from the North (Pak Chong). Here are many restaurants, hotels and resorts catering to the visitors staying overnight.
After paying a 400 Baht entry fee, we could drive into the park. We were met by a group of macaques, ostentatiously trying to look inside the car to see if we had something to eat.
The visitor center is in the middle of the park. It has a small display of the park's history and nature. And two stuffed tigers.
Outside the building, a short trail starts that leads you through the forest to the small Kong Kaew Falls. It's a nice and easy walk of about 45 minutes.
For more serious walking my driver left me at Pha Kluai Mai Campsite, promising to pick me up again some kilometers down the road at Haew Suwat Falls. The walking trail leading there is said to be 3 kilometers long. Although the path is quite clear, I found it rather tough going because you have to climb under or over fallen trees a lot.
After about two-thirds of the way I took a wrong turn, that directed me along/into a small creek. The birds are brilliant here; they scream ('a big white foreigner is coming') and flee to the higher treetops. I see bright green cockatoos and ones with long blue feathers.
As I cannot find any trace of a path anymore, I decide to retrace my steps. A good move, because suddenly I see where I've missed a turn. Instead of following the creek, I had to cross it via two huge fallen trees (they're laid down like a bridge). The trail from there is easy again. It follows the main river. A large white (crane-like) bird speeds past just above the water surface.
After two hours I reach the end of the walking trail, where my driver is waiting for me.
We leave Khao Yai at the south exit, passing an area with many elephants. They sometimes cross the road (warning signs tell us), but we only see their droppings.