Pha Sok

Pha Sok is a natural rock pool at the edge of a sandstone cliff inside Pha Taem National Park, looking out over the Mekong River and the hills of Laos beyond. Khong Chiam district, where the park sits, is Thailand’s easternmost point — the Mekong marks the border here, so the view from the cliff edge looks directly across the river into Lao territory. Pha Sok is one of the featured stops on the Ubon Ratchathani Geopark trail, and it only holds water — and only opens to visitors — during the rainy season, roughly mid-July through November; the rest of the year the site is closed.

The name comes from the Isan word sok, meaning a groove or channel worn into rock by long use — either water erosion or a footpath trodden for generations. That’s exactly what water has carved into this stretch of sandstone: trenches and basins deep enough that the cliff-edge pool has earned the local nickname “the floating sky jacuzzi.”

Visiting isn’t as simple as walking up. Pha Taem park staff require visitors to register in person at park headquarters with a national ID card or passport before entering the Pha Sok area, and the site caps numbers at 100 people a day for day trips and 30 for anyone camping overnight. Call the park office (045-252-581) ahead of a visit to confirm the site is open and check the current quota.

Watch out: Because access is seasonal and permit-controlled, don’t build a Pha Taem itinerary around Pha Sok without checking first — the park has announced closures as early as late November in past years, and the pool simply isn’t there to see in the dry season.

Insider Tip: Bring long socks or gaiters — leeches are common on the approach trail after rain, which is exactly the condition that fills the pool. Pack drinking water and sun protection too; there’s no shop at the site itself.

Standard Pha Taem National Park entry applies — 40 THB for Thai visitors, 200 THB for foreigners — on top of the free Pha Sok registration. The site sits in Huai Phai subdistrict, Khong Chiam district, alongside the park’s better-known viewpoints; Sao Chaliang’s balanced rock formations and the Two-Colour River viewpoint where the Mekong meets the Mun are both a short drive away, inside Ubon Ratchathani province.