These hold a surprising variety and number of wildlife, from elephants and a dozen species of primates to hundreds of bird species.
Here are some of the best places on the mainland to experience nature, of which Kaeng Krachan, Khao Yai and Khao Sok are our top three.
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Khao Yai National Park
Khao Yai National Park was the very first in Thailand and is its most popular, being a short day-trip from Bangkok.
Don’t let that put you off, as its vast size (800 square miles) means it’s easy to get away from the crowds even on weekends.
Now recognised as a Unesco World Heritage Site, it encloses one of the largest intact monsoon forests in mainland Asia but is better known for its 40 waterfalls, one of which featured in the Leonardo DiCaprio film “The Beach”.
You can hike in the jungle, perhaps spotting elephants but almost certainly deer and macaques.
You’re also unlikely to see the leopards and tigers that live deep in the jungle but you will hopefully enjoy the 400 bird species.
A number of guesthouses of all standards have sprung up nearby – there is even a wine trail in the area – but overnight options also include camping.
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Doi Inthanon National Park
Doi Inthanon includes the country's highest mountain and has been dubbed “the roof of Thailand”.
Its terrain varies from tropical lowland below 2,5000 feet to more than 8,000 feet, where temperatures as low as -17ºF have been recorded.
At higher altitudes, there can be rain at any time of year and this is the place to see cloudforest, with epiphytes (plants that take their moisture from the air, rather than roots) and some rare orchids. The park also has Thailand’s greatest variety of birds, including such rarities as the Ashy-throated Leaf-warbler and green-tailed Sunbird which are found nowhere else in the country.
The hill tribes of the region have left a number of trails which hikers can now follow. Major sights include Mae Ya Waterfall, the highest in Thailand, and the more visited Mae Klang Waterfall where you can swim.
Brichinda Cave is another popular excursion from Chiang Mai. There are a number of guesthouses and two campsites, where tents can be rented.
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Erawan National Park
This national park near the “Bridge on the River Kwai” town of Kanchanaburi – and the border with Burma – is home to more than 300 bird species.
The most common include the dark-necked tailorbird, blue whistling thrush and crested serpent eagle.
Tree platforms are a good way to spot canopy birds such as the great hornbill, as well as some of the many macaques and even gibbons that live in this lush, hilly jungle.
Other animals you might hope to see include Indian muntjac, elephant, boar and the antelope-like serow. There are a number of hiking trails in the forest and another major attraction is the Erawan Falls.
It gives its name to the park, being named after a three-headed white elephant from Hindu mythology because its top tier resembles an elephant’s head covered in a white veil of water.
The falls descend in a series of seven pools that are popular for bathing and picnicking.
Huai Kha Khaeng Wildlife Sanctuary
Huai Kha Khaeng and nearby Thung Yai Wildlife Sanctuary together make up the largest protected mainland wildlife area in Southeast Asia, recognised on Unesco’s World Heritage List.
It’s home to Thailand’s largest population of tigers, although sightings are rare. However, elephants, boars, leopards and several species of deer are common sights as the relatively open woodland makes spotting them easier than in other reserves.
There are several large rivers, bordered by grasslands that merge into hillier terrain covered with light deciduous and bamboo forest.
It is home to many rare and endangered species, including Thailand’s largest population of banteng, a form of wild cattle.
The sanctuary is also one of the country’s best birdwatching destinations, with several watchtowers and self-guided trails. Hikes on longer trails need to be accompanied a ranger, partly to protect against wild elephants.
Mae Wong National Park
Hilly Mae Wong goes up to the peak of Khao Mo Ko Chu, at almost 4,500 feet and is a good place for trekking.
Some walks take a few hours, others a few days with a trek to the summit of Khao Mo Ko Chu being a five-day effort.
Long and short trials will take you to waterfalls deep in the forest and birdwatchers consider it one of the best spots in Thailand: up to 450 species have been spotted. The high altitudes make a warm layer advisable.
This is one of the remotest parks and a great place for a complete escape into nature.
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Khao Sok National Park
Khao Sok is within reach of the popular holiday destinations of Phuket, Krabi, Khao Lak and Koh Samui, making it one of Thailand’s most popular.
That’s despite it being one of the wettest places in the country (the best time to visit is in the dry season between June and October). The monsoon rains help support a diverse range of flora and fauna, including Rafflesia kerrii.
This, the world’s largest flower, is famed for its smell of rotten meat and is found only in this park and a few similar habitats in Malaysia.
You can explore the park by canoe or on foot along hiking trails in the dense rainforest that may give glimpses of animals such as deer, elephants, boar and tapirs as well as hundreds of bird species.
This region was heavily logged at one time but Khao Sok became a guerrilla hideout in the 1970s, which kept out loggers, poachers and miners until the park was established in 1980.
Despite this, a dam was built across the Pasaeng River in 1982, creating Cheow Larn Lake and wiping out many of the park’s species, particularly fish.
Even so, there remain around 50 mammal and 30 bat species as well as many reptiles, including frogs, toads, lizards and snakes. The island-rich lake is now a popular destination in its own right where you can stay overnight on a raft house.
Luxurious (OK, they have showers and toilets) treehouses in the jungle canopy are another adventurous alternative.
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Kaeng Krachan National Park
Thailand’s largest national park is bordered to the west by Tanintharyi Nature Reserve in Burma, from which visitors are banned.
The resulting large expanse of rainforest supports leopards, bears, elephants and, allegedly, the Sumatran rhinocero. This smallest of rhinos is thought to be extinct in Thailand, with only 100 left anywhere on earth, but rumours persist it has been seen near the Burmese border.
You are much more likely to spot one of the 400 birds – including kingfishers and hornbills – or 300 butterfly species for which the park is well known.
The Ban Krang campsite has a saltlick that attracts some solitary wild elephants and is also noted for its birdlife. A few miles away are the Hua Chang and twin Khao Pakarang Caves, the latter of which has a bat population.
Phanoen Thung Camp is at a higher altitude and offers the chance to see birds such as hawks, eagles and the Asian barbet.
Hikes in the forest require a guide but it also has many easily accessible waterfalls, including the 11-tier Pala-U which is a common place to spot wild elephants. The park’s two rivers are also pleasant spots for a less energetic boat ride.
Kui Buri National Park
Not far from Kaeng Krachan is Kui Buri, famed for its elephants and with viewing platforms being set up near watering ponds offering a good chance of seeing them.
Although you can drive through certain areas, visitors can only tour protected zones with a guide in the park’s own FWD vehicles.
It’s well worth it to hear the history of the park and be guided to a view of the wild elephants. The relatively open landscape makes it easier to spot animals, but also for them to spot you. Guest bungalows and tents are available to hire for those who want to spend the night.
Khao Sam Roi Yot National Park
This park on the Gulf of Thailand is remarkable for the variety of habitats, from beach and mangrove to mountains and caves.
The park’s name refers to the “300 Peaks” of its limestone mountains, which are rich in caves. These include sunlit Praya Nakorn cave which has a beautiful Buddhist pavilion often visited by the Thai monarchy, and the striking stalactites and stalagmites of Sai Cave.
The mangrove waterlands are an important stopover for migrating birds with January and February being the best months to see them.
A kayak or boat tour with a guide is the best way to explore these waterways, where you might see fishing cats, and the mangrove boardwalk allows you to get even closer to nature.
The forests host some other 300 bird species as well as crab-eating macaques, dusky langurs, serows and barking deer. You can also camp on the mile-long sandy beach for the perfect tropical experience.