All of the literature about Kao Yai says to visit during the rainy season because that's when the waterfalls are at their best. But, a warning always follows saying be careful of the leeches who want to suck your blood.
Sure enough, when we arrived at the visitor's center (after paying respects to the spirit of Kao Yai of course) we were advised to buy anti-leech "socks" for 70 baht ($US1.80) a pair. The socks were supposed to be worn in your shoes and over your pants all the way to your knees. Piyawat wore his, I figured my hiking boots with my long pants tucked in would give me enough protection.
I was wrong. After a short 1 KM hike through the woods, we returned to the visitor's center, had lunch, and got back in the car to go to the campground. Halfway there I felt something crawling up my leg. I reached down and to my horror realized it was a leech heading towards my .... !
Piyawat pulled over and I quickly took off my shoes and now-bloody socks. I found two other leeches who were drinking blood through my socks and one leech on my waist. Ewww!
After removing the leeches we headed to the campground, rented a tent and set it up. Then we drove to a nearby waterfall called Heaw Suwat. The waterfall is a famous one, as it was used in the movie The Beach with Leonardo DiCaprio, and it was as beautiful as advertised. Since I now was wearing the leech socks, we headed back into the steamy jungle and hiked to another nearby waterfall. We returned hot and sweaty and very dirty, but with big smiles on our faces (and no leaches!)