The vast majority of planet Earth is covered with deep, dark waters with new and exciting mysteries waiting to be discovered every day.

Rivers, lakes and the ocean floor have only partially been explored, and all kinds of incredible underwater landscapes and creatures have been found. But some of the most bizarre underwater finds have nothing to do with nature and natural phenomenon. From long lost cities to unidentified objects, searching the depths of our oceans has given scientists insights into the past, the present and the downright strange.

Some of the craziest underwater finds aren’t long-forgotten ancient wonders, or treasures that have fallen foul of Mother Nature’s fury, such as shipwrecks laden precious metals. Some have been very deliberately placed, from deep sea art galleries to oceanic crematoriums.

There are tons of crazy things lurking in the deep, and here are 25 pics of just a few of them. These, of course, are just a drop in the ocean - we can’t even begin to guess what else might be lurking underneath the water.

25 25. An Ancient Greek Computer

A 2,000-year-old vessel discovered off the coast of a Greek island unearthed a wealth of treasures, from vases and jewellery to a bronze statue. But there was one object that stumped archeologists at the time - it would take another 100 years for scientists to finally understand the importance of this object.

Now known as the Antikythera mechanism, archeologists now believe this is arguably the world’s first computer, according to Vox. With its two dozen gears, intricately positioned on top of one another, it was apparent that the mechanism was some sort of calculating device. It’s now though that it was used to predict the position of the planets and stars in the sky, depending on the calendar month.

After nine months of work, the world’s first semi-submerged art gallery opened at the Fairmont Resort in the Maldives in 2018. Known as The Coraliarium, it was the work of British sculptor Jason deCaires Taylor and designed as an homage to sea life and the coral house reef surrounding the resort.

The gallery was a steel cube with 30 life-size sculptures within it. Some stood at tidal level, while others were beneath the ocean. Later that year, however, the sculpture museum was destroyed after the government deemed it inappropriate, according to The Independent.

23 23. One of The World's Most Beautiful Shipwrecks: The Sweepstakes, Canada

According to the United Nations, there are around three million shipwrecks lining the ocean floor and the Sweepstakes, which lies just 20ft below the surface of Ontario Lake, might be one of the most beautiful.

This 19th-century schooner was built in 1867, according to the Daily Mail. She was hauling coal near Cove Island when she sustained damage to her hull, and a decision was made to sink her in 1885. Sweepstakes is now an attraction for divers and tourists in the Fathom Five National Marine Park.

22 22. More Than 60 Tons Of WWII Silver

In November 1942, the SS City of Cairo was sunk by a German U-boat while carrying 296 civilians and cargo that included 100 tons of silver. It went undiscovered until 2011 when the team at Deep Ocean Search found it off the coast of Ireland. Among its many finds were about 100 tons of silver, which would be worth about $50 million in today’s money, according to CNN.

The coins were melted and sold, with Deep Ocean Search getting a percentage of the sale, along with the UK Treasury, the BBC reported.

21 21. Underwater Museum of Art, Florida

The first underwater museum in the United States opened in 2018 off the coast of Grayton Beach State Park in Florida. The aquatic sculpture park was a collaboration between the Cultural Arts Alliance of Walton County and South Walton Artificial Reef Association, an organisation created to raise awareness of ocean vulnerability in the wake of the Deepwater Horizon oil spill.

According to CNN, the park has seven sculptures, including an oversized pineapple and human skull, including works by artists Vince Tatum and Allison Wickey.

20 20. Apollo 11 Engines In The Atlantic Ocean

The mighty engines that helped deliver man to the moon in 1969 were discovered in the Atlantic Ocean in 2012. In a search led by billionaire Amazon chief executive and space enthusiast Jeff Bezos, the huge Saturn V rockets were discovered lying 14,000 feet below the surface, reported The Guardian, along with dozens of other artefacts, including thrust chambers, gas generators, injectors, heat exchangers, turbines and fuel manifolds.

19 19. The Unexplained Yonaguni Underwater Pyramid, Japan

There are giant stone structures lying just below the waters off Yonaguni Jima and scientists can’t agree whether they’re the remains of a lost Japanese Atlantis, or entirely natural formations.

Masaaki Kimura, a marine geologist at the University of the Ryukyus in Japan, who has dived the site for more than 15 years, is convinced they are the ruins of a 5,000-year-old city.  According to National Geographic, he claimed: “The largest structure looks like a complicated, monolithic, stepped pyramid that rises from a depth of 25 meters."

However, not everyone agrees and Robert Schoch, a professor of science and mathematics at Boston University, has dismissed claims that these structures are manmade, believing them to be entirely natural sandstone formations. The mystery continues.

18 18. Haul Of Valuable Emeralds Off The Coast Of Florida

It’s the plot of a Hollywood movie, involving treasure maps and sunken treasure - 10,000 emeralds were discovered by an amateur treasure hunter in 2010, off the coast of Florida.

The price of the jewels, found by Jay Miscovich, was estimated at half a billion dollars but it wasn’t a simple tale of finders keepers. In fact, it wasn’t a simple tale at all.

Not only did the origins of these gemstones mystify just about everyone, but a court order also granted Miscovich temporary ownership of the jewels which made it illegal for him to sell them. In a stunning twist, it later emerged that the whole thing had been a hoax, and the owner of a jewellery store in Jupiter, Florida, testified that Miscovich had bought 80 pounds of rough emeralds just before the ‘discovery’ was made.

17 17. The Cannons Of Famous Pirate Blackbeard

First discovered in 1996, the ship of infamous pirate Blackbeard, the Queen Anne’s Revenge, was discovered off the coast of North Carolina and became a hotbed for archeological activity.

In 2013, researchers retrieved five cannons from the wreck, each weighing between 2,000 and 3,000 pounds, according to the Huffington Post. The Queen Anne’s Revenge is believed to have been kitted out with a massive 40 cannons, and although it’s unlikely that all of them will be recovered, other artefacts discovered include anchors, gold dust, animal bones, lead shot, plus medical and scientific instruments.

16 16. An Atlantis-Themed Underwater Crematory

With its ancient-looking statues, gates, columns and stone roads, the Neptune Memorial Reef looks more like a sunken necropolis than a crematorium. Make no mistake, however, because this underwater crematory off the coast of Key Biscayne, Florida can accommodate the ashes of up to 4,000 individuals.

The undersea cemetery was designed by Florida artist Kim Brandell and opened in 2007, and doubles up as an artificial reef, where divers can explore and loved ones can visit, according to Atlas Obscura.

15 15. The BVI Art Reef, British Virgin Islands

The tentacles of a kraken gripping onto a WWII era ship is the unforgettable sight that awaits divers visiting the BVI Art Reef. Off the coast of Virgin Gorda, this art installation was opened in 2017 by billionaire and Virgin Island resident Richard Branson, a big supporter of the project.

The ship, the Kodiak Queen, isone of five surviving ships from the attack on Pearl Harbor, according to Bloomberg and has now become a man-made marine ecosystem, along with an 80-foot-long Kraken sculpture.

14 14. Arachnophobes Beware: Underwater Spiders

If you’re scared of spiders, you might have thought you’d be safe in the water. However, the diving bell spider, which is native to freshwater habitats in Europe and Asia, spends its entire life underwater.

It does so by building its own diving bell, like the chambers early divers used to breathe underwater. According to National Geographic, the spiders spin a dome-shaped web between underwater plants, before rising to the surface to trap air bubbles using fine hairs on their legs and belly. The spiders fill the dome with these bubbles, creating a bigger bubble that they can fit inside. No matter how you feel about spiders, that’s pretty amazing.

13 13. She Cheng Underwater City, China

Sometimes called the “Atlantis of the East,” Shicheng is a magnificent 600-year-old metropolis and a brilliantly preserved example of Imperial Chinese architecture. But you’ll have to dive 40 metres underwater to visit it.

The Chinese authorities deliberately flooded the city in 1959 to make way for the Xin’an Dam and its adjoining hydroelectric station. At the bottom of what is now called Qiandao Lake lies in-tact stone architecture, including preserved stonework of lions, dragons, phoenixes and city walls which are believed to date back to the 16th Century.

According to the BBC, the Chinese government organised an expedition in 2001 to see what might remain of the once great city.

12 12. A Locomotive Graveyard In New Jersey

Under 90 feet of water, off the coast of New Jersey, lie two steam locomotives from the 1850s. Discovered in 1985, during ocean mapping, the trains appear to be a rare Planet Class 2-2-2 T, but seeing as there is absolutely no record of them, it’s a mystery as to how they got there.

According to the Daily Mail, the most likely theory is that they were being transported from Boston to the Mid-Atlantic on a barge when they encountered a storm. The engines either fell off by accident, or were deliberately pushed off to lighten the ship.

11 11. Underwater Government Meetings In The Maldives

In 2009, the Maldivian president, Mohamed Nasheed, and his government ministers held the world’s first underwater cabinet meeting. This headline-grabbing event was designed to highlight the risks posed to the world's oceans by climate change, according to Reuters. If United Nations predictions are correct, most of the Maldives will be submerged by 2100.

“We are trying to send our message to let the world know what is happening and what will happen to the Maldives if climate change isn’t checked,” Nasheed told reporters.

10 10. Museo Atlántico In the Canary Islands

This eerie sunken world, featuring more than 300 individual sculptures, is the brainchild of artist and naturalist Jason deCaires Taylor. Located off the coast of Coloradas Bay in Lanzarote, Museo Atlántico was Europe’s first underwater art gallery when it opened in 2016.

The amazingly detailed figures are 12 to 14 metres under the surface and the whole project took three years of planning. The installations, which also function as an artificial reef, are designed to provoke environmental awareness and social change, reported The Guardian.

9 9. The Ghost Fleet Of Chuuk Lagoon

Under the clear blue waters of Chuuk Lagoon in the South Pacific lies the biggest graveyard of ships in the world. During WWII, the lagoon was home to Japan’s Imperial Fleet, which was destroyed after a two-day Allied bombing campaign known as Operation Hailstone.

These days the site is one of the best dives spots in the world for WWII wrecks, and divers can explore the ghostly remains of hundreds of Japanese aircraft and other military machines.

8 8. The Unexplained Skeletons Of Roopkund Lake

Roopkund Lake is located in the Indian Himalayas, 16,000 feet above sea level, surrounded by nothing but frozen glaciers and ice-capped peaks. But for one month a year, when the lake’s ice thaws, the remains of more than 300 people are revealed, understandably earning Roopkund the nickname of Skeleton Lake.

Scientists and historians have tried to unravel this mystery since the remains were first discovered in 1942. In 2004, Oxford University's Radiocarbon Accelerator Unit conducted radiocarbon dating on the remains and concluded that they date back to around 850 AD. As there is no evidence of a nearby settlement, it is believed that the individuals were travelling when they perished. How exactly they met their demise, however, remains a mystery.

7 7. The Lost City In The Gulf of Khambhat (Which Might Be The Oldest City In The World)

Archaeological remains discovered 36 metres underwater in the Gulf of Cambay, off the western coast of India, could radically rewrite what historians and archeologists know about human civilisation.

Discovered by accident in 2001 by oceanographers from India's National Institute of Ocean Technology, the ancient remains of this vast city are believed to predate the oldest known remains in the subcontinent by more than 5,000 years, according to the BBC. Providing further work on the site verifies initial test results, this ancient site could have massive repercussions for our view of the ancient world. Crazy.

6 6. Mysterious Giant Eye Ball

Imagine strolling along the beach only to spot a huge, squishy eye floating in the sea. This weird scenario happened to one beachcomber on Florida’s Pompano Beach, who handed their bizarre find over to the Florida Fish and Wildlife Conservation Commission.

Scientists used genetic testing to identify the owner of the massive eyeball, according to Business Insider, and based on the eyeball's "color, size and structure, along with the presence of bone around it,” they concluded is most likely came from a swordfish.