In Thai, khao yai means "big mountain", and indeed Khao Yai is one of Thailand's largest, most popular, and grandest national parks.
Also Thailand's first officially protected national park (it was established in 1962) and both an ASEAN Heritage Park and UNESCO natural heritage site, Khao Yai spans some 2,168 square kilometres spread over parts of Nakhon Ratchasima, Saraburi, Prachinburi and Nakhon Nayok provinces.
The park's vast territory is home to some of Thailand's last remaining wild tigers, leopards, gibbons, exotic snakes and elephants. It is also a very popular destination with bird watchers as it hosts over 300 species of birds.
As its name would suggest, the park is relatively high up in the mountains with its highest peak -- Khao Rom -- reaching over 1,350 metres. The park has five vegetation zones from grassy plains to evergreen rainforest, and it can get quite cool in the higher altitudes.
Perhaps Khao Yai's biggest draw are its 44 waterfalls, including a couple considered to be among Thailand's most impressive. There are also some spectacular viewpoints, wildlife observation towers, roaring rapids, tranquil streams, and rugged trails under thick jungle canopy.
If you've a serious interest in national parks in Thailand, Khao Yai, along with Kaeng Krachan to the south of Bangkok, should be on your short list.
While the park is oval shaped with its east to west width stretching farther than its north to south height, the entire eastern half of the park is free of roads and the only trails to be found here are those originally made by elephants.
While many of these trails have been maintained to varying degrees by park officials, the eastern half of Khao Yai is truly a wild place, so it's absolutely vital that visitors enlist a ranger before venturing too far out. In fact, even the more frequented trails in the park's western half are not always clearly marked, so if you're not an experienced outdoors person, you might consider hiring a guide if looking to do some serious hiking.
At the very least, never venture in to the forest late in the afternoon -- the middle of the jungle is not a place you want to spend the night.
The most frequented entrance to Khao Yai is at the end of Thanarat Rd south of Pak Chong, with the other entrance in Nakhon Nayok province to the south. Route 2090 is the main road running north to south that cuts through Khao Yai's western half, and there are a few paved side roads off 2090 that lead to some of the more popular waterfalls and viewpoints, as well as campgrounds and lodges.
The first thing you'll see after entering the park from the north is a small temple dedicated to Chapaw Khao Yai, which translates to "the god of Khao Yai". If you're the superstitious type, light three sticks of incense along with the locals and hopefully compel the residing spirit of the area to keep you safe in the park.
For some reason, visitors do not receive a map or information brochure upon entering the park. These -- along with everything you'll need for your Khao Yai adventure -- may only be obtained at the Visitor Centre located towards the middle of the park's western half along the main road. Here, English speaking park officials provide information on everything from attractions and trails to finding a place to sleep.
Night safaris may be arranged here and park certified guides may be hired at a rate of 500 baht per three hours. Along with an excellent museum that opened in 2012 and has fossils, stunning photography, videos and other info, a cafeteria, coffee stand and convenience store selling basic necessities are all clustered around the Visitor Centre. The main lodging area is also found here, set back near a small waterfall.
Another area of lodging is found towards the south of the park, closer to the Nakhon Nayok entrance, and two campgrounds are spaced near each other right in the heart of the park's western half along the main roads, a couple of kilometres south of the Visitor Centre. There is another restaurant and convenience shop found here, as well as the tourist police office. The Tourist police may be reached any time by calling (044) 341 7778.
There are four convenience shops selling basic necessities in Khao Yai from 07:00 to 19:00. One is beside the Visitor Centre cafeteria, another near Lam Takong campground, a third at the site of Pha Kluai campground, and the last near the Zone 4 accommodation area. Each of these places also have restaurants open from 7:00 to just 16:00, so make sure to stock up on Mama noodles and cookies for the late night!
There are no banks or ATMs in Khao Yai National Park, but there are a few located within a kilometre of the gates on Thanarat Rd. There are also no filling stations in the park, so be sure to fill up your motorbike or car before hand if taking your own wheels.
While there is a very basic medical dispensary at the Visitor Centre, anything serious will require going to Pak Chong. There is also no Internet available within the park, but a decent 3G cell signal is usually accessible near the main roads.
Khao Yai's gates are open from 6:00 to 21:00 daily. Admission is 400B for foreigners and 50B for Thai citizens. There is an extra 50B charge if bringing a car into the park, and it's also worth nothing that unlike some of Thailand's national parks, a ticket to Khao Yai is only valid for one entry, so while a single ticket is valid for as long as you wish to stay in the park, if you leave you'll need to pay for a whole new ticket in order to re-enter (maybe they took some pointers from the immigration ministry?).
Once inside the park, signs along the roads to the main attractions and services are plentiful and reasonably well placed.