One of Thailand's most valuable nature preserves, Nam Nao National Park covers 966 sq km across the Phetchabun Mountains of Chaiyaphum and Phetchabun Provinces. Hiking trails branch out from the visitor centre to several scenic overlooks. Haewsai Waterfall is 17km east of the visitor centre, while to the west lie the best sunrise/morning fog (5km) and sunset (11km) viewpoints. When the park is busy, vehicles (70B per person) deliver people to the viewpoints; reserve a seat at the visitor centre.
With an average elevation of 800m, temperatures are fairly cool year-round (nám nŏw means 'cold-feeling water') and frost can occur in December and January. There are both evergreen and deciduous forests, including some three-leaf pine, uncommon in Thailand, mixed with some vast bamboo groves. Nam Nao lies at the heart of the Western Isaan Forest Complex, a 6000-sq-km block of eight connected preserves (including Phu Kradueng National Park and Phu Khiaw Wildlife Sanctuary; permits must be acquired in advance to visit the latter), so wildlife is particularly abundant. Elephant encounters are common enough that there's an electric fence around the campground. Lucky visitors might also spot Malayan sun bears, banteng (wild cattle), Asian jackals, barking deer, gibbons, pangolins and flying squirrels. There are even a few tigers. More than 200 species of birds, including great hornbill and silver pheasant, fly through the forest, and the exceptional visibility makes this one of Thailand's best birdwatching sites.
Although it covers remote territory (this remained a People's Liberation Army of Thailand stronghold until the early 1980s), Hwy 12 makes for access easy. Most buses heading west to Lom Sak or Phitsanulok from the ordinary bus terminal in Khon Kaen (120B, 2½ hours) will stop in the park. The visitor centre is 1.5km from the highway.