A 2900km sq part of the Western Forest Complex which runs along the Thai-Burma border, Kaeng Krachan has probably the greatest variety of wildlife in Thailand. Wildlife viewing here is good, camping is good, and there are stunning mountain views at a second 4WD-access camp.
The park can be done independently, but realistically, you need either a vehicle or a guide to get in. And if you want a guide, get the best, from Tontan Travel.