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.