Koh Rong is Cambodia’s island escape, and it still has the rough edges that make it feel like a discovery rather than a resort. The main beach — Long Set, also called Long Beach — is four kilometres of white sand backed by jungle, with beach bars that range from bamboo shacks to something approaching comfort. Development is coming, you can see it in the half-built concrete at the edges, but for now the island retains its castaway character. I arrived on the morning ferry from Sihanoukville, stepped off the boat onto a wooden pier, and within ten minutes had my feet in sand so white it looked artificial. It is not.
We hiked across the island through dense jungle to Lonely Beach, where we were entirely alone for an afternoon. The trail is unmarked in places, the jungle thick enough that the canopy blocks the sky, and the heat inside the tree cover is a physical thing — a wall of humidity that makes every step feel earned. When the trees open and the beach appears — a crescent of white sand, turquoise water, no one — the relief is total. We swam, ate the mangoes we had carried, and watched hermit crabs negotiate the tide line with an urgency that seemed comic against the stillness of everything else.
The snorkelling off the quieter southern bays revealed healthy coral and curious fish — parrotfish, clownfish, the occasional barracuda holding motionless in the current like a silver blade. The reef is not Maldives-grade, but it is alive and accessible and free of the crowds that have ruined snorkelling in much of Thailand. We rented masks from a shack on the beach and swam out from shore, no boat required, and spent two hours drifting over coral gardens that started in waist-deep water.
But the headline experience is the bioluminescence. On moonless nights, the plankton in the shallows light up electric blue with every movement, and swimming through them is genuinely otherworldly. I waded in up to my chest and moved my arms slowly, and the water erupted in constellations around my fingers. Each stroke left a trail of blue light that faded over seconds. I have never experienced anything like it, and I say that as someone who has chased northern lights and swum with whale sharks. This was more intimate, more strange, more like being inside a phenomenon rather than observing one. Koh Rong Sanloem, the smaller sister island, offers a quieter alternative with better-maintained beaches and a dive school that takes you to sites most visitors never reach.
When to go: November to May is dry season. December to February is peak but manageable. Avoid September and October when rough seas can cancel ferries. Bioluminescence is best on dark, moonless nights.