Cool and lush, Khao Yai National Park is an easy escape into the primordial jungle. The 2168-sq-km park, part of a Unesco World Heritage site, spans five forest types teeming with wildlife. There are good hiking trails and some fantastic waterfalls including Nam Tok Haew Suwat and Nam Tok Haew Narok that put on thundering shows in the rainy season.
The park is the primary residence of, among many others, shy tigers and elephants, noisy gibbons, colourful tropical birds, massive pythons and countless audible, yet invisible, insects. Khao Yai is a major birding destination, with large flocks of hornbills and hundreds of other birds. In the grasslands batik-printed butterflies dissect flowers with their surgical tongues and semi-tame deer graze with little care about nearby shutterbugs.
Visiting independently is quite easy as the English-speaking staff at the visitor centre are very helpful, motorcycles can be hired, and visitors with cars are usually happy to pick up pedestrians; though tours are reasonably priced and easy to arrange.
There are five marked trails for independent walking, but birders or animal trackers should consider hiring a jungle guide to increase their species count (the guides here are excellent) and appreciation of the environment.
Early-morning and early-evening visits to the roadside salt licks and the Nong Pak Chee Observation Tower sometimes provide close encounters with elephants, guar, and other large mammals, though the night safaris (reserve at the visitor centre) are the best wildlife-watching opportunity. It's important to understand that spotting the park's elephants and smaller critters is considered a bonus, with most people happy just to admire the mature jungle and frothy waterfalls that blanket and drain the peaks of Big Mountain.