Protected from the ravages of the Andaman Sea by Phuket, AO PHANG NGA has a seascape both bizarre and beautiful. Covering some four hundred square kilometres of coast between Phuket and Krabi, the mangrove-edged bay is spiked with limestone karst formations up to 300m in height, jungle-clad and craggily profiled. This is Thailand’s own version of Vietnam’s world-famous Ha Long Bay, reminiscent too of Guilin’s scenery in China, and much of it is now preserved as national park. The bay is thought to have been formed about twelve thousand years ago when a dramatic rise in sea level flooded the summits of mountain ranges, which over millions of years had been eroded by an acidic mixture of atmospheric carbon dioxide and rainwater. Some of these karst islands have been further eroded in such a way that they are now hollow, hiding secret lagoons or hongs that can only be accessed at certain tides and only by kayak. The main hong islands are in the western and eastern bay areas – to the west or east of Ko Yao Noi, which sits roughly midway between Phuket and Krabi. But the most famous scenery is in the central bay area, which boasts the biggest concentration of karst islands, and the weirdest rock formations.
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Hongs are the pièce de résistance of Ao Phang Nga: invisible to any passing vessel, these secret tidal lagoons are enclosed within the core of seemingly impenetrable limestone outcrops, accessible via murky tunnels that can only be navigated at certain tides in kayaks small enough to slip beneath and between low-lying rocky overhangs. Like the karsts themselves, the hongs have taken millions of years to form, with the softer limestone hollowed out from above by the wind and the rain, and from the side by the pounding waves. Eventually, when the two hollows met, the heart of the karst was able to fill with water via the wave-eroded passageway at sea level, creating a lagoon. The world inside these roofless hollows is an extraordinary one, protected from the open bay by a ring of cliff faces hung with vertiginous prehistoric-looking gardens of upside-down cycads, twisted bonsai palms and tangled ferns. And as the tide withdraws, the hong’s resident creatures emerge to forage on the muddy floor, among them fiddler crabs, mudskippers, dusky langurs and crab-eating macaques, with white-bellied sea eagles often hovering overhead.