Sam Phan Bok

Sam Phan Bok - 'three thousand holes' - surfaces each dry season on the Mekong in Ubon Ratchathani, when the falling river uncovers what is billed as the largest rock reef along its course: a sandstone shelf drilled by millennia of whirlpool-driven gravel into thousands of smooth potholes, basins and winding channels. Locals point out the shapes - a dog, a star, a famous mouse-eared silhouette - while photographers wait for the low sun, when the whole sculpted field glows amber and every hole fills with shadow. Longtail boats run the channel beneath carved cliffs, and swimming holes warm in the shallower basins. In the wet season the river simply takes it all back, metres under the current. The reef lies on Thailand's far eastern edge, hours from the tourist trail, anchoring an Isan loop of river confluences, cliff paintings and slow-boat country.

What you actually see

• The pothole fields - thousands of water-carved sculptures underfoot.
• The named shapes - the dog, the star and the mouse-eared silhouette.
• Golden hour - low sun turning the reef to amber sculpture.
• The longtail run - the river channel beneath carved sandstone cliffs.

When to go

December to May, when the Mekong drops; January to April exposes the most rock. Come at dawn or in the last two hours of light - for the glow and against the heat.

Honest expectations

There is no shade and the rock bakes - carry water and skip midday. In the wet season the site literally does not exist above water. Facilities are village-basic and the drive is long; make it part of an Isan itinerary, not a detour.

Nearby

Khong Chiam's two-river confluence, Pha Taem's cliff paintings and Ubon Ratchathani.