Phu Chong–Na Yoi was established in 1987, covering 428,750 rai — roughly 686 square kilometres — across the Buntharik, Na Chaluai, and Nam Yuen districts of Ubon Ratchathani Province. It is designated IUCN Category II, the same classification as most national parks worldwide: a protected area managed primarily to preserve natural ecosystems and provide a base for scientific research and environmental education.

The park sits at the eastern terminus of the Dângrêk Range, the same mountain chain that further west defines the Thai-Cambodian border and shelters the ruins at Preah Vihear. Here, the mountains dwindle toward the Mekong basin, and the park's terrain reflects that transition — a mix of elevated forest, river valleys, and the dramatic cliff formations that mark where the plateau meets the lower ground of both Laos and Cambodia.

The park's most visited natural feature is Namtok Huai Luang, also known as Namtok Bak Teo — a waterfall that drops from an elevation of 30 metres in three distinct stages. Below the last step, a small pool forms beside a white sand beach, its water running turquoise. That combination — the sound of falling water, the unexpected white sand, the colour of the pool — draws visitors consistently through the rainy season, when the flow is at its strongest.

Nine kilometres south along the nature trail, Namtok Koeng Mae Phong offers a quieter alternative, fed by the Lam Dom Noi Stream rather than the main Huai Luang watercourse. Between the two waterfalls, the trail passes through Kaeng Sila Thip, where the Huai Luang Stream runs across a broad rock terrace. The current here carved holes of varying size and depth into the rock surface over centuries — formations the locals call *kumphalak*.

The Phlan Yao Rock Garden is not a garden in any cultivated sense. It is a stretch of terrain where rocks in different formations have accumulated naturally, scattered across the ground in arrangements that suggest something deliberate without being so. The Pha Phueng Viewpoint stands adjacent to it, offering views across the forest canopy toward the international border.

Further on, Phlan Kong Kwian — the Cart Terrace — is a vast flat rock surface edged by stone shelters. Travellers in earlier centuries stopped here to rest; the name records that history. Wild flowers and plants grow in the cracks and depressions across the terrace. The sense of the place as a waypoint persists, even though the travellers who sheltered here were moving between kingdoms that no longer exist in the same form.

In 2004, a researcher working in Phu Chong–Na Yoi collected a specimen that turned out to belong to a species unknown to science. The frog, later named *Fejervarya triora*, was formally described in a 2006 paper titled "Three New Species of Frogs and a New Tadpole from Eastern Thailand." It belongs to the genus *Fejervarya*, a group of ditch frogs distributed widely across South and Southeast Asia, but this particular species had never been identified before.

A national park of 686 square kilometres on a mountainous border harbouring an animal that science had not yet named is a reminder of how much the forest still contains. The park's terrain — forest that moves freely across the Thai, Lao, and Cambodian sides of a porous border — creates exactly the kind of continuous habitat where undescribed species persist. *Fejervarya triora* was found here. There is no particular reason to think it was the only one waiting to be found.