Khao Yai National Park

Listen first. Before you look for anything, just listen. A long, rising whoop drifts across the treetops, then another answers it from further away. That sound is gibbons calling to each other at the start of the day. Under your feet the ground is soft with fallen leaves, and the air smells of damp bark and green growth. The light comes down in narrow shafts through the forest. Welcome to Khao Yai.

The name is simple. In Thai, Khao Yai means big mountain. That fits the landscape you are standing in. It is a high, folded block of hills and plateaus on the southwestern edge of the Khorat Plateau, the large raised tableland that covers much of northeastern Thailand. Most visitors arrive from the city of Nakhon Ratchasima or from Bangkok. The roads climb steadily, the temperature drops, and the rice fields give way to forest.

Here is the first fact many visitors miss. Khao Yai was Thailand's very first national park. It was declared in 1962, at a time when much of the country's lowland forest was being cleared for farms. The park protects a huge area of forest and grassland that stretches across four provinces: Nakhon Ratchasima, Saraburi, Prachinburi and Nakhon Nayok. In total, it covers more than two thousand square kilometres. You could drive for an hour inside it and still only see a small corner.

The protection did not stop at the park boundary. In 2005, UNESCO listed Khao Yai as part of a larger World Heritage Site called the Dong Phayayen–Khao Yai Forest Complex. This chain of protected forests runs eastward toward the Cambodian border. Together, these forests shelter a remarkable range of animals and plants. Some of them are rare across the rest of mainland Southeast Asia. For conservation in Thailand, this place matters a great deal.

The forest itself changes as you move through it. In the lower valleys you find tall evergreen trees, with thick vines hanging from their branches and buttress roots spreading out like stone walls at their base. Higher up, the forest becomes cooler and mistier. In other areas, open grassland lets you see far across the hills. These open patches are important. Deer and other grazing animals come out to feed there, especially in the early morning and late afternoon.

Now the animals. Khao Yai is one of the best places in Thailand to see wild Asian elephants. A herd lives in the park, and the elephants often walk along the main roads, especially at dusk. If you meet them, stay in your vehicle, keep your engine running, and give them plenty of space. These are wild animals, not performers. Sambar deer, barking deer and pig-tailed macaques are also common. The macaques often sit by the roadside. Please do not feed them — it changes their behaviour and makes them aggressive.

Look up as well. Khao Yai is famous among birdwatchers for its hornbills. These large birds have huge curved bills topped by a hollow structure called a casque. You often hear a hornbill before you see it. Its wingbeats make a loud whooshing sound, a bit like a steam engine passing overhead. The great hornbill is the largest of them, with black and white wings and a yellow-topped bill. Hornbills depend on big, old trees for nesting, so their presence is a good sign of healthy forest.

That whooping sound from the start belongs to gibbons. These small apes have no tail, very long arms, and they swing through the branches with great speed. Two kinds of gibbon live in this park, and their ranges meet here. That is the second surprise. In a few places, the two kinds even mix and produce hybrid young. Gibbon pairs sing duets together, usually in the morning, to mark their territory. If you hear one, stop and stay quiet. The song can last many minutes.

Water shapes this park too. Rivers cut down through the hills and fall over rocky ledges in a series of waterfalls. Haew Narok is one of the most dramatic. It drops in tiers down a steep cliff, and you reach the viewpoint by walking down a long staircase. Haew Suwat is smaller but wider. It falls as a single curtain into a pool below. Film fans may recognise it, because it appeared in the movie The Beach, released in 2000.

The waterfalls change a lot through the year. In the rainy season, roughly from the middle of the year into autumn, they are loud and full, and the spray drifts across the path. In the dry months they become thinner, and some almost stop. The rainy season also brings leeches to the forest trails. They are harmless but unpleasant. Many visitors wear leech socks, which are tall cloth socks pulled up over the trousers. Rangers and local guides can show you which trails are open.

As you walk, notice the textures around you. The bark of the big trees is covered in moss and small ferns. Strangler figs wrap around other trees, slowly growing down to the ground. Termite mounds rise from the forest floor like small clay towers. The air feels heavy and wet under the canopy, then suddenly lighter when you step into a clearing. Cicadas fill the background with a high, steady buzz that rises and falls with the heat of the day.

Outside the park, the area around Khao Yai has grown into a popular weekend escape for people from Bangkok. You will pass resorts, cafés, farms and even vineyards along the approach roads. The cool hill climate makes this possible. It creates an interesting contrast. Inside the park gates, the focus is on silence and wildlife. Outside, the roads fill with weekend traffic. Coming early in the morning, or on a weekday, lets you feel the forest at its quietest.

Before you move on, pause for a moment where you are. Look at the layers of green in front of you: the ferns at your feet, the vines in the middle, and the high canopy above. Listen for a bird call or the creak of branches in the wind. This forest has been protected for more than sixty years. As you walk back, keep your eyes on the edges of the road. Something may be watching you from the trees.