Oceans cover more than 70% of the Earth’s surface, containing roughly 97% of our water – and are an endless source of fascination. We know some of the creatures that dwell in the deep, from plankton to blue whales. We’ve seen pictures of the enormous Great Barrier Reef and of vast icy landscapes with icebergs and glaciers. Yet more than 80% remains unexplored, and still further swathes are rarely seen. Here we virtually plunge into the most mysterious parts of our watery world.

Greenland is home to thousands of icebergs. Some form from frozen saltwater while others – like these, scattered at the mouth of the Ilulissat Icefjord – break or ‘calve’ from glaciers and drift into the ocean.

These icebergs, which make up a UNESCO Heritage Site, have drifted from fast-moving Sermeq Kujalleq. It calves off more ice than any glacier outside Antarctica and is responsible for forming around 10% of Greenland’s icebergs.

A maelstrom is, in essence, a very powerful whirlpool or ‘crushing current’. But that doesn’t quite do justice to the sheer force of the maelstrom that swirls and spins at high speeds in the Saltstraumen sound in Norway. It’s officially the world’s strongest tidal current, reaching speeds up to 23 miles per hour (37kmph), or 20 knots in nautical terms.

The whirlpool is fed by waters flowing fast and heavily in and out of a narrow strait that connects two fjords. It’s hard to imagine that any creatures could survive in or even close to waters throttling at such speeds, yet Saltstraumen is teeming with marine creatures from monkfish to huge blue Atlantic wolffish.

The smattering of hundreds of tiny islands that make up Palau, an archipelago in the Pacific Ocean, are surrounded by a marine sanctuary and home to some of the world’s most intriguing underwater dwellers. Among the weirdest – and most wonderful – is the nautilus, an elegant mollusc distantly related to squids and the octopus.

Its shell is a veritable palace, with several compartments within a labyrinthine structure. The nautilus lives in the largest chamber and expels water from its body into the surrounding ‘rooms’, giving it the buoyancy that makes it such a fabulous swimmer.

Off the coast of Key Largo in the Florida Keys, this state park encompasses around 70 nautical miles of the Atlantic Ocean – and some of the most ethereal underwater scenes. It was established as a state park in 1963 to protect part of the only living coral reef in the continental US, making it the country’s first undersea park.

Its waters are filled with fascination and beauty, from sea turtles and shimmering schools of minnows to parrotfish and huge star coral structures. There are also several shipwrecks, which have become encrusted with coral, and man-made touches like Christ of the Abyss, a bronze statue 25 feet (7.6m) below the water’s surface. Discover more underwater sculptures, shipwrecks and more, here.

As if icebergs weren’t awesome enough already, throw in some stripes and marbling, and they’re almost too dazzling. The patterns form when cracks appear in the icy mass and are flooded with seawater that freezes.

One of the world’s most remote marine sanctuaries lies off the coast of the US territory of American Samoa, whose verdant archipelago is clustered in the South Pacific Ocean. Beneath the surface is the Fagatele Bay coral reef, which was almost destroyed by crown-of-thorns starfish before becoming protected in 1986.

The sanctuary started off as just a quarter of a mile (0.4km) and has expanded to cover 13,581 square miles (35,175sqkm). It encompasses vibrantly colourful reefs with more than 150 species of coral and home to green sea turtles, hundreds of species of fish, and humpback whales.

Christmas tree worms are actually relatively common, although their appearance is anything but. These spindly, spiny creatures, photographed here near the Cayman Islands archipelago, live on tropical reefs and remain in the same spot for most of their lives. Each has two crowns that look like Christmas trees, in colours from pale yellow to magenta and cobalt blue.

Between the East China Sea and the Pacific Ocean, these ‘Iseki’ stones were discovered around 1986 off the remote Japanese island of Yonaguni. The rock structures lurk 82 feet (25m) below the surface and include tall monoliths, stacked slabs and a pyramid, which is the largest shape.

Mystery – and plenty of debate – shrouds the structures’ origins. Some claim they are naturally occurring geological formations shaped by tectonic activity and others are convinced they are the remains of an ancient city. People say they are the ruins of man-made buildings including a castle and a stadium that once formed a Japanese Atlantis.

Deep-dwelling glass sponges may look soft, squidgy and, in the case of this Euplectella species, as pretty as spun sugar. But they’re also known as ‘venus flower baskets’ because they are, to the tiny shrimp that live inside them, prisons. While the crustaceans’ offspring leave to find their own sponges, their parents eventually grow too large to escape and remain there for the rest of their lives.

On the margins of the Arctic Ocean north of Alaska and west of the US state’s Arctic islands, this remote sea is frozen solid all year round apart from in August and September. During these months, the ice around the coast cracks to reveal strips of water scattered with bergs and floes.

While it looks like a desolate, frozen wasteland, the sea’s ice and small islands provide an important habitat for wildlife including polar bears and Peary caribou. The water itself is home to beluga and bowhead whales. Now take a look at these amazing photos of inspiring sights from around the world.

Lurking in the waters around Spiadan, the bumphead parrotfish is remarkable for more than its size, unusual appearance and frankly terrifying teeth. It’s also responsible for keeping the tiny Malaysian island’s beaches glistening white – with its waste. The fish use their tough beaks to scrape algae from coral and rocks, ingesting some of the hard substances which are excreted as powder-soft white sand.

This archipelago is officially part of Norway, but it’s a pretty significant 580 or so miles (930km) north of the country’s tip, and feels a world away from anywhere. In fact, its snow-blanketed islands, icebergs and ice floes seem to belong to another planet altogether. They also belong to the polar bears.

The word Svalbard means ‘cold coasts’ which is certainly apt. The islands are laced by fjords and surrounded by glaciers that jut into the Arctic Ocean, where frigid waters are studded dramatically with icebergs and arches. Discover the last unspoiled places on Earth here.

Not a museum in any traditional sense but the sculptures lurking off the coast of Crimea are as fascinating as anything encased in glass and kept in the world’s hallowed institutions. The so-called ‘Alley of Leaders’ was curated in 1992 by diver Vladimir Borumensky, who dropped statues and busts of communist leaders – including Lenin (pictured), Stalin and Marx – into the sea at Cape Tarkhankut. Find more striking communist remains around the world here.

Stranded in the Atlantic Ocean more than 1,000 miles (1,609km) east of the tip of South America, South Georgia Island is wonderfully remote, allowing millions of penguins to thrive. It’s a habitat for king, gentoo and macaroni penguins, the latter sporting flamboyant, punky blond crests.

In total, this isolated speck of an island is home to more than 10 million birds, who live and breed among the rugged landscape of snowy peaks, black mountains and blue glaciers. Otherworldly creatures sharing the island include albatrosses, reindeer and elephant seals.

The world’s largest island, Greenland’s coastline is littered, in the loveliest way, by icebergs that lend an ethereal air to the waters surrounding it. These crisp blue formations were captured at sunrise in the Greenland Sea, part of the Arctic Ocean.

In the depths of the Pacific Ocean off the coast of the Hawaiian islands of Maui, Kauai and Oahu, this little-known sanctuary provides an important protected habitat. You'll find humpback whales and other marine life here including sea turtles, endangered Hawaiian monk seals and spinner dolphins, famous for incredible acrobatic displays.

The waters that lap the shores of the pristine Chagos islands, 932 miles (1,500km) south of India, are vivid with coral reefs and even bolder, brighter marine life. The archipelago consists of 55 teeny-tiny islands, which are dwarfed by life beneath the surface of the Indian Ocean they’re scattered across.

The seawater is the cleanest ever recorded, according to the Zoological Society of London, which works with a team on the ground (or in the water) to study the tropical coral reefs and their abundance of marine creatures, from thresher sharks to spinner dolphins. It’s also home to the world’s largest living coral atoll, the Great Chagos Bank, and the endemic brain coral (pictured).

The Antarctic has around 93% of the world’s icebergs and Pleneau Bay, in the Wilhelm archipelago, is rich in the dramatic ice sculptures, earning it the nickname ‘Iceberg Alley’. It’s also home to what is, less cheerily, known as the ’Iceberg Graveyard’, where structures from various locations have drifted and hit ground. Take a look at these jaw-dropping photos which show the beautiful and terrifying power of Mother Nature.

This ‘lost’ sunken city is hidden under the water’s surface not far from the more famous ruins of Pompeii. Baia was another ancient Roman town that fell victim to volcanic activity but, instead of being buried under lava flow, the town was abandoned before parts were submerged by the rising water level.

Strewn with fine statues, columns and walls adorned with frescoes, it seems more like an incredible submarine sculpture park than a former city. From around 100 BC until around AD 500, Baia was the fabulously rich playground of the Roman elite, including one Julius Caesar, who had a villa there. These are the world's most incredible Roman ruins you have to see to believe.

Indonesia’s Komodo National Park is best known for the enormous namesake komodo dragon lizards that the preserve was set up to protect. But the waters around the Lesser Sunda Islands, across which the park is based, contain an equally beguiling world of mangrove forests, seagrasses and coral reefs teeming with rare and wonderfully odd marine creatures.

The biodiverse area, part of what’s known as the ‘coral triangle’, contains around 1,000 species of fish and 260 types of coral. Among the fascinating animals that call the reef gardens home are pygmy seahorses, manta rays, dugongs – which are sometimes called sea cows and look similar to manatees – and these rather delicious-sounding chocolate chip starfish.

This oceanic trench – a narrow, deep-sided depression on the ocean floor – is the deepest known in the Southern Hemisphere and the second deepest on the planet, after the Mariana Trench in the western Pacific. Located on the edge of the Tonga Ridge in the South Pacific, its average depth is 20,000 feet (6,000m), plunging to a head-spinning 35,702 feet (10,882m) in places. It’s home to diverse and fascinating marine creatures from sperm whales to sea cucumbers.

Chuuk (or Truk) Lagoon, deep below the water’s surface off the coast of the Caroline Islands, in the South Pacific, is an eerie graveyard littered with battleships, air crafts, submarines, helmets and gas masks. These are the poignant remnants of Operation Hailstone, a two-day attack on Japan’s Imperial Fleet in 1944, which killed thousands of soldiers and became known as Japan’s Pearl Harbor.

The site remained undiscovered until the 1960s, when legendary ocean explorer Jacques Cousteau found it. The hundreds of rusting structures are now encrusted in coral that’s home to a vibrant array of marine creatures – bringing new life and colour, and somehow adding to the ethereal beauty. Now take a look at these stunning photos of the world's most spectacular shipwrecks.

This iceberg-strewn lagoon is tucked on the edge of Iceland’s southeastern coast, where it meets the North Atlantic Ocean. Part of Vatnajökull National Park, the glacial water is home to hundreds of hunks of ice shuffling and creaking in a mesmerising slow dance. Many are streaked with blue, green and black. Now check out the world's most beautiful natural wonders.