A constant topic of conversation among divers is where they have been before, and where they're planning to go next. With old favorites competing with newly discovered destinations, Asia Pacific spoils divers for choice when it comes to the next big underwater adventure. Not all of our top 20 iconic sites will appeal to everyone (and there's plenty of room to argue those we may have omitted!), but these 20 sites are surefire highlights of any Asia-Pacific scuba diving trip. READ MORE: The Most Epic WWII Wrecks for Scuba Diving 20. Cod Hole, Great Barrier Reef, Australia

Cod Hole, Great Barrier Reef, Australia Christian Loader/Scubazoo

Arguably one of the world's most famous sites, Cod Hole owes its popularity to divers' perpetual fascination with the huge, friendly fish that live here. Growing up to two metres long, the cod are formidable in size but their doleful, almost human facial expressions make it difficult to be apprehensive around them, particularly as they are not shy about approaching divers in the hope of a free meal. Cod Hole has plenty of other fish species living amongst the site's coral bommies and walls, but it's undoubtedly the cod themselves that remain in the memory long afterwards.

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19. Carl's Ultimate, Eastern Fields, Papua New Guinea

Carl's Ultimate, Eastern Fields, Papua New Guinea Julian Cohen

If you have dived all over the world in search of dream sites, only somewhere truly spectacular would qualify as best. Carl Roessler, a pioneer in the dive travel industry, made that discovery on one of the world's most remote reefs, Eastern Fields in Papua New Guinea. Legend has it that Carl was so stunned by what he saw that he asked the boat captain to mark the then unnamed site on the map as Carl's Ultimate. A huge underwater ridge covered with a profusion of sea fans, soft corals and crinoids, Carl's Ultimate catches the changing, nutrient-rich currents, which bring literally thousands of fish streaming across the reef in an electric blaze of vivid colour and synchronised, swift movement. Many divers make the pilgrimage to PNG for this site alone, and after multiple dives here, they'd gladly do it all again. 18. Busselton Jetty, Western Australia

Busselton Jetty, Western Australia Mick Tait

Busselton Jetty juts out well over a kilometre into the Indian Ocean from its namesake town in southwest Australia. First built in 1845, its presence over the last 170 years has created a new universe between the girders below. Masses of colourful soft-coral fronds encrust the jetty's struts, while huge schools of fish hover between them seeking shelter, making it a real fish-bowl experience. The marine life is so rich that an underwater observatory was built so nondivers could see 8 metres beneath the jetty for themselves. 17. Nudi Falls, Lembeh Strait, Indonesia

Nudi Falls, Lembeh Strait, Indonesia Paul Whitehead

It's a challenge to single out just one iconic dive site at Indonesia's Lembeh Strait, given how every one of them can yield a breathtaking array of otherwise impossible-to-find critters. But Nudi Falls is a firm favourite for any nudibranch enthusiast, given the sheer abundance of the colourful sea slugs found on its gray sand slopes, each one a tiny explosion of colour and pattern against the muted background. Elsewhere in the world you'll be lucky to spot one or two tiny nudibranchs; at Nudi Falls you'll fill up your camera's memory card with them. 16. Rainbow Warrior, Cavalli Islands, New Zealand

Rainbow Warrior, Cavalli Islands, New Zealand Richard Robinson

Environmental organisation Greenpeace's original ship, Rainbow Warrior was sunk in Auckland harbour in 1985 by French secret service agents. Subsequently moved and scuttled in the Cavalli Islands two years later, the Rainbow Warrior sits upright with a maximum depth of 27 metres. That leaves plenty of time to explore the wreck, which has become a thriving artificial reef covered with colourful jewel anemones and home to resident schools of bigeye and mackerel. 15. Kapalai House Reef, Malaysian Borneo

Kapalai House Reef, Malaysian Borneo Christian Loader/Scubazoo

Often overlooked in the excitement over neighboring Sipadan, Sipadan-Kapalai Resort's house reef is one of Asia-Pacific's hidden gems. The resort itself is stunning, built entirely on stilts on a sandbank in the middle of the Celebes Sea. It's this unique setup that gives divers access to the shallow, sandy house reef, which is ideal for long, leisurely macro-hunting dives. Kapalai's jetty and several small wrecks are all part of the house reef, providing perfect cover for rare creatures like the flamboyant cuttlefish and blue-ring octopus, as well as mandarinfish mating at sunset. 14. Cannibal Rock, Komodo, Indonesia

Cannibal Rock, Komodo, Indonesia Brenda Blackburn

Few dive site names capture a sense of untamed wilderness as well as Cannibal Rock, named for a Komodo dragon seen devouring one of its own on a nearby beach. Cannibal Rock lies within southern Komodo's Horseshoe Bay, a beautiful and wild U-shaped tract of water that provides safe harbour for ships and marine life alike. The dive site itself is a large mound rising up from the bottom, layered with wave upon tangled wave of soft and hard corals, amongst which lurk giant frogfish and monster nudibranchs, while massive schools of fish race around the rock's curves. while the site often needs a 5 mm wetsuit to be enjoyed properly, there's so much life here that divers won't notice the chill. 13. Rangali Madivaru, Ari Atoll, Maldives

Rangali Madivaru, Ari Atoll, Maldives Chris Mitchell

There are plenty of places to see manta rays in the Maldives, but at Rangali Madivaru all the elements combine to make conditions near perfect. A shallow ridge at around 20 metres, there are actually several manta-cleaning stations along its top, and the visibility is reliably a Maldivian sun-drenched blue. Divers can position themselves beneath the cleaning stations on the ridge, leaving the mata rays undisturbed and thus likely to stay for much longer. It's not uncommon to have four or five giant mantas wheeling around the stations for an hour or more, leaving even the most jaded divers smiling through their regulators. 12. German Channel, Palau

German Channel, Palau Wendy Capili-Wilkie

A shipping channel hewn through the reef early in the 20th century to connect an inner lagoon with the outside ocean, the southwest opening of German Channel has strong currents, which daily bring manta rays to the cleaning stations at the channel's edge. Sometimes the mantas rise up and playfully engage in barrel rolls over the heads of dazzled divers. The mantas aren't the only marine life riding the currents — sharks skitter around the sandy bottom and big schools of trevallies and snappers gather at the channel's opening, making this a continually head-turning dive. 11. Blue Corner, Palau

Blue Corner, Palau Wendy Capili-Wilkie

You can sum up Palau's Blue Corner in a single word: epic. The very definition of an adrenaline dive, Blue Corner's large plateau has dramatic dropoffs on all sides patrolled by scores of grey reef sharks. Reef hooks are mandatory to float in the current and watch the sharks cruise by, coming ever closer, before unhooking and being swept back across the plateau into hundred-strong schools of barracuda, tuna, trevallies, jacks and curious Napoleon wrasse. The whole site is a perpetual cauldron of marine activity that is simply breathtaking.

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10. Monad Shoal, Malapascua, Philippines

Monad Shoal, Malapascua, Philippines Jun Lao

Monad Shoal is one of the few places in the world where divers stand a chance of seeing the elusive thresher shark, instantly recognisable by its elegant, tapered tail. Hit the water very early for the best chance of an encounter and wait. It's eerie but exhilarating to patiently pause at the edge of the dive site's dropoff and suddenly see the unmistakable shape of a thresher shark emerge from the early morning gloom. The elegance and power with which they move is a sight not soon forgotten. 9. Roma, Southeast Sulawesi (Wakatobi), Indonesia

Roma, Southeast Sulawesi (Wakatobi), Indonesia Courtesy of Wakatobi Dive Resort

Roma is the ultimate sampler site. This broad pinnacle rises to within 10 feet of the surface, with a dense hard coral cover that harbors blue ribbon eels, dwarf pegasus seamoths, leaf scorpionfish, crocodilefish, octopuses, cuttlefish, winged pipefish, rockmover wrasses, nudibranchs and more. An extensive grove of pavona coral is swarmed by anthias, redtooth triggerfish, fusiliers and convict blennies. The steep side of the formation is fringed with table corals, soft coralsW and fans. Deeper, large barrel sponges lead the way to Roma’s signature coral formation: a gigantic turbinaria coral that resembles a rose in bloom. Dive This Now: Wakatobi Dive Resort 8. Kwatisore, Cenderawasih Bay, Indonesia

Kwatisore, Cenderawasih Bay, Indonesia Chris Mitchell

Only recently discovered by divers, Cenderawasih Bay is a vast body of water in Indonesia's remote Papua region. Fishermen from the tiny village of Kwatisore have set up floating platforms from which to attach their nets, and they've attracted a very special visitor — the biggest fish in the world. Whale sharks cruise beneath the platforms to feed, and it's not just an occasional sighting of a solitary diner — there can be six or seven whale sharks circling one platform for hours on end, allowing divers some incredible up-close moments with these 8-metre giants. 7. Shark Airport, Tubbataha Reef, Philippines

Shark Airport, Tubbataha Reef, Philippines David Fleetham

Tubbataha Reef's remote atolls in the Sulu Sea are only accessible for a few months each year, which ensures the reef's dive sites are a haven for some species that are endangered elsewhere. The aptly named Shark Airport is a case in point — a wide shallow plateau that drops off to a slope, it's a site where close encounters with numerous patrolling whitetip sharks are common. Mantas also occasionally appear out of the blue and big schools of jacks and trevallies run the gauntlet with the sharks, while hawksbill and green turtles are usually found munching the coral in the shallows. 6. Hardeep Wreck, Pattaya, Thailand

Hardeep Wreck, Pattaya, Thailand Chris Mitchell

There's no getting around it: With usually poor visibility and sometimes vicious currents, Hardeep is a challenging shipwreck to dive. But for dedicated wreck divers, it's worth the effort — this WWII ship was sunk by an RAF B24 Liberator squadron off the east coast of Thailand in 1945, and lies on its side at around 25 metres. Its positioning means that its side portholes now form an arching roof, which dramatically streams light down on divers penetrating the wide-open hull. Seventy years of coral is encrusted around every railing and shard of metal, making the Hardeep a truly evocative dive. 5. Richelieu Rock, Phuket, Thailand

Richelieu Rock, Phuket, Thailand Chris Mitchell

There's little argument that Richelieu Rock is Thailand's finest dive site. Lauded by Jacques Cousteau in the late 1980s, Richelieu continues to captivate divers three decades later thanks to an endless array of marine life that gathers around the horseshoe-shaped pinnacle 200 km northwest of Phuket. The interior of the rock provides safety from the strong ocean currents, letting harlequin shrimp and ghost pipefish live amongst the cracks and fissures. The outside of the rock is covered in verdant soft corals and baitfish, with big schools of snapper and barracuda hanging in the blue. The rock also occasionally plays host to manta rays even passing whale sharks. 4. Maaya Thila, Ari Atoll, Maldives

Maaya Thila, Ari Atoll, Maldives Jason Isley/Scubazoo

Part of a strictly enforced marine reserve, Maaya Thila is a sloping, layered pinnacle that starts at only six metres. The thila's shallow flat top and numerous overhangs and caves makes it a tremendous site for spotting whitetip sharks patrolling, turtles resting and metre-wide stingrays hoovering across the coral. Schools of tuna, barracuda and Moorish idols prefer the larger caves, while plenty of macro critters like mantis shrimp also nestle within the thila's many fissures. 3. Shinkoku Maru, Truk Lagoon, Chuuk

Shinkoku Maru, Truk Lagoon, Chuuk Todd Winner

Part of the WWII Japanese war fleet sunk in 1944 at the remote Pacific atoll of Chuuk during Operation Hailstorm, the huge oil tanker Shinkoko Maru sits upright and at its shallowest is only 11 metres from the surface. The delicate pink, red and yellow soft corals that cling to every surface have softened the ship's hard steel lines over time. So many fish gather around the wreck that it can sometimes be hard to discern its outline, but the massive interior's walkways, engine room and navigation bridge still show sobering reminders of those who lived and died on the ship. 2. Cathedral Rock (aka Boo Rock) Raja Ampat, Indonesia

Cathedral Rock (aka Boo Rock) Raja Ampat, Indonesia Debi Henshaw

Cathedral Rock is dominated by two massive windows in the limestone rock, carved out over time by the strong currents that can thunder through this site. Located at Raja Ampat's Boo Island, the windows stand guardian over a breathtakingly rich reef, with hard and soft corals growing on top of each other in a tumbledown profusion of colour and texture. Swirling around the reef in a continually dynamic display are swarms of blue-flash fusiliers, yellow snapper and unicornfish, while the resident school of batfish seems to hover stationary and unconcerned amongst the frenetic activity. 1. Big Mushroom, Green Island, Taiwan

Big Mushroom, Green Island, Taiwan Thomas Konig