Forty-two uninhabited limestone karsts rise vertically from the Gulf of Thailand, their sheer cliffs protecting a 102-square-kilometer marine sanctuary that remained closed to commercial development until 1980. Mu Ko Ang Thong National Marine Park, established on November 12 that year, preserves one of Southeast Asia's most intact archipelago ecosystems — a labyrinth of hidden lagoons, submerged coral gardens, and mangrove-fringed coves where Brahminy kites and white-bellied sea eagles nest undisturbed. The park's geological signature is its karst topography, sculpted over millennia by monsoon rains that carved vertical fissures and sea caves into the Permian-era limestone. Talay Nai, the Emerald Lagoon on Ko Mae Ko, sits 250 meters inland, its jade-green water separated from the sea by a knife-edge ridge only 50 meters wide. The lagoon's salinity matches the ocean's despite no visible connection — geologists attribute this to subterranean channels permeating the porous bedrock. A 500-step climb from the beach delivers panoramic views across the entire archipelago, the limestone towers arrayed like chess pieces on a turquoise board. Beneath the surface, visibility routinely exceeds 15 meters during the dry season from December through April. The shallow coral reefs surrounding Ko Wao, Ko Tai Plao, and Ko Sam Sao host over 50 recorded coral species, including staghorn, brain, and table corals that shelter parrotfish, butterflyfish, and blacktip reef sharks. Snorkeling sites concentrate along the eastern flanks of the islands, where nutrient-rich currents from the open gulf sustain dense fish populations. Kayaking routes thread through sea arches and tidal channels too narrow for motorized craft, granting access to mangrove stands where mudskippers climb exposed roots and monitor lizards patrol the shoreline. The park enforces a 300-baht conservation fee for foreign adults, collected at the headquarters on Ko Wua Talap where a network of trails ascends to a viewpoint 240 meters above sea level. The ranger station maintains daily visitor logs dating to 1984, tracking seasonal fluctuations in arrival patterns — February and March see the lowest rainfall and calmest seas. Operating hours run from 08:00 to 18:00 daily, with the last speedboat departures from mainland piers occurring by 09:30 to allow full-day itineraries before the return crossing. Tour operators include the conservation fee within their quoted rates alongside lunch, snorkeling equipment, and kayak rentals.