Hin Daeng / Hin Muang

Hin Daeng and Hin Muang are two isolated pinnacles rising from deep water in the southern Andaman Sea, at the far south of Mu Ko Lanta National Park. Hin Daeng breaks the surface as a small rock and drops in steep walls and ridges to beyond 50–60 m; Hin Muang, lying roughly 500 m to the southwest, is fully submerged (its summit at about 8 m) and forms what is widely described as Thailand's tallest vertical wall, falling away past 60–70 m into the blue. Both are draped in dense soft-coral growth — predominantly red at Hin Daeng and vivid purple at Hin Muang — and surrounded by schooling pelagics. Their exposed, offshore position channels nutrient-rich current onto the rocks, which is what draws large oceanic manta rays (up to about 4 m wingspan) and whale sharks, most reliably from February through April. There is no land or mooring shelter, so surface conditions can be rough and currents moderate to strong; the sites are best suited to experienced divers (operators typically require Advanced certification or 50+ logged dives). They are reached as a long day trip by speedboat from Koh Lanta (about 1.5–2 hours) or by Andaman liveaboard. Because they sit within Mu Ko Lanta National Park, the offshore islands and pinnacles are officially closed during the southwest monsoon (16 May–15 November), so diving runs roughly mid-November to mid-May.

• Hin Daeng and Hin Muang are widely rated the best dive sites accessible from Koh Lanta and among the finest in Thailand, prized for steep soft-coral walls and big-animal encounters. Hin Daeng is named 'Red Rock' for its red soft corals and Hin Muang 'Purple Rock' for its purple ones; the two pinnacles lie only about 500 m apart, so a single trip normally dives both.
• Hin Muang is described as the highest vertical wall in Thailand: its summit sits around 8 m below the surface and the wall drops away to roughly 60–70 m, putting the deeper face well below recreational limits and making strict depth and gas discipline essential.
• The exposed pinnacles offer Thailand's best combined odds of oceanic manta rays and whale sharks. Whale sharks can appear in any open month but encounters peak from early February to late April, and oceanic mantas (up to about 4 m across) gather to feed in the current, most reliably January through April.