Richelieu Rock

Richelieu Rock sits about 14 kilometres east of the Surin Islands, rising from open water as a horseshoe-shaped limestone pinnacle — and if you've dived much of the Andaman, you'll quickly understand why divers talk about it the way they do.

The rock tops out at around two metres below the surface and drops to roughly 35 metres on its deeper flanks, with the most productive diving happening between 10 and 25 metres. Visibility averages 10 to 20 metres, though current can sweep through hard, especially around the pinnacle's outer edges, so you'll want some experience reading water movement before you head here.

The marine life is genuinely exceptional for a single site. Whale sharks pass through between February and May — I've had encounters here that lasted 20 minutes, which is rare anywhere. Beyond that headline, the rock is carpeted in sea fans, wire coral, and soft coral that hosts thorough populations of seahorses, ghost pipefish, and nudibranchs if you slow down and look properly.

Schooling barracuda, giant grouper, and thick aggregations of trevally are a given. Manta rays show up irregularly, usually following plankton blooms.

Reef condition is broadly healthy compared to much of Thailand — the site benefits from its remote location and national park status — though occasional bleaching events have touched the shallower sections. Moorings are in place to prevent anchor damage, which is encouraging.

Almost all access is via liveaboard from Khao Lak, typically on three-to-seven night itineraries that combine Richelieu with the Similans and Koh Bon. Day boats from Khao Lak occasionally run here but it's a long haul. No snorkelling operations visit regularly.

Best visited November to May; open-water certified minimum, though Advanced certification is strongly recommended given the currents.