Richelieu Rock

Richelieu Rock is Thailand's consensus number one, an isolated horseshoe of limestone in open sea whose every surface is upholstered in magenta soft coral. The site runs both ends of the scale simultaneously: glassfish and snapper in humming walls, trevally and Spanish mackerel cutting lanes through them, seasonal whale sharks looming out of the plankton haze between roughly February and April, while inches from the rock, tigertail seahorses, harlequin shrimp, ornate ghost pipefish, and frogfish carry the macro program. Multiple dives here on one trip are standard and never redundant. Current, crowds, and brilliance arrive together; all three are part of the experience.

The moment you come for: Purple soft-coral pinnacle, seasonal whale sharks, world-class macro on the same rock

Topography: Limestone pinnacle cluster wrapped in purple soft coral

Current: Current sets the day's plan; the horseshoe's inner curve gives shelter while the outer faces fly.

Entry: Reached by liveaboard or long-range day boat; the horseshoe barely breaks the surface at low tide and dives are tide-planned.

Hazards: Strong current and boat congestion at the moorings; watch the blue on ascent for traffic.

Permits & rules: Park fees apply; the site closes with the annual mid-May to mid-October park closure.

Conservation: Within Thailand's marine national park system with fees and mooring rules; no gloves, no contact with the dressed rock.

Nitrox: Worth it here — profiles sit in the range where enriched air meaningfully extends no-stop time (with the training to use it).