More than 70 percent of our planet is covered by water, yet an enormous 80 percent of this remains unexplored and unmapped, according to the US National Ocean Service. In short, there are tons of crazy things lurking in the deep.

From surprising geological formations and natural phenomenon, to creatures that defy imagination, new technological advancements mean that scientists are discovering amazing things every year - and that’s just the work of Mother Nature. Many wonders of the underwater world aren’t even native to the big blue. Shipwrecks, entire cities and treasure are just some of the incredible man-made things that lie on the seabed, waiting to be found.

Not all things wait to be found, however. Plenty of crazy and cool stuff has washed up on shores across the globe. Whether it’s love letters, whale vomit, or giant Lego men, these items certainly raise questions and, in some cases, can even provide the answers to previously unknown mysteries.

Read our list of strange ocean discoveries, some of which even made it on to shore, and be reminded of just how mysterious a place the ocean still can be.

25 25. Underwater: The Engines Of The Apollo 11 Mission

Off the coast of Florida, some 14,000 feet under water, the engines from the Saturn V rocket, which launched Neil Armstrong into outer space on the Apollo 11 mission, were discovered after 43 years.

The man who discovered these incredible artefacts of modern history was none other than Jeff Bezos, CEO of Amazon, who also funded the expedition. Bezos, it turns out, is a bit of a space geek and, according to The Guardian, he credits the Apollo 11 mission with fuelling his passion for science and engineering.

24 14. Underwater: The "Ice Finger Of Death"

It’s been dubbed as the “Ice Finger of Death,” which sounds pretty ominous. The reality is that brinicles, as they’re more commonly known, are actually more fascinating than scary.

Discovered in the 1960s, these underwater icicles are formed when sea ice cracks and leaks out saline water. Because this saline water is denser than the water around it, it sinks to the ocean floor, and freezes the fresher water it comes into contact with.

When a brinicle reaches the sea floor, it catches any creatures it comes into contact with, such as sea urchins and starfish - hence its sinister nickname.

According to MNN, scientists think these brinicles may even foster conditions that could sustain life on other planets and moons, such as Jupiter’s Ganymede.

23 21. Underwater: Elongated Skulls In A Mexican Sinkhole

Sac Uayum is a cenote located in Mexico’s Yucatán Peninsula. It’s a place that locals feared and in 2012, a team of divers discovered the reason behind its fearsome reputation.

An underwater survey discovered two chambers of the cenote littered with human bones, including deformed skulls. As the National Geographic explains, the skulls most likely got there because of human sacrifice. The shape of the skulls, with the top of the cranium flattened, was an intentional method of deformation practiced by the ancient Maya. No wonder local residents got bad vibes.

22 20. Underwater: The Mysterious Yonaguni Complex, Japan

First discovered by a dive tour operator back in 1985, this ancient structure has sparked heated debate among scientists. Masaaki Kimura, a marine geologist at the University of the Ryukyus in Japan, believes it to be the ruins of a Japanese Atlantis, sunk by an earthquake 2,000 years ago, according to the National Geographic.

But not all researchers are convinced it’s even manmade, claiming, instead, that’s it’s merely a natural formation. The debate rages on.

21 19. Underwater: The Baltic Sea Anomaly

It kind of looks like the Millennium Falcon from Star Wars, and some corners of the internet have been keen to claim it as a possible UFO discovery, but what exactly the Baltic Sea Anomaly is has yet to officially be identified.

The Swedish-based Ocean X Team discovered the anomaly in 2012, and while scientists from Stockholm University carried out analysis on samples and concluded that it is simply a glacial deposit, the team remains unconvinced, according to Live Science. The anomaly remains unexplained to this day.

20 18. Underwater: The Sunken City Of Dwarka

Dwarka is one of the best-studied underwater sites in India and it’s considered as one of the four Dhamas, a sacred place of pilgrimage, in the Hindu religion. Sanskrit literature identities Dwarka as the city once founded by Lord Krishna.

Located on the Gujarat’s west coast, in northwestern India, the site is all the more remarkable because it’s thought to be 9,000 years old, which pre-dates known Indian civilization by some 4,000 years, according to the New Indian Express.

19 17. Underwater: The Silfra Crack

Have you ever wanted to dive in the crack between the North American and Eurasian continents? Yeah, sure. Who hasn’t? It might sound odd, but this is literally achievable at the Silfra Crack in Iceland’s Thingvellir National Park.

The Silfra fissure was formed in the divergent tectonic boundary between the North American and Eurasian plates, which drift about 2cm further apart every year. The water in the rift is some of the clearest in the world, according to the Huffington Post, making it one of the most popular natural attractions in Iceland.

18 16. Underwater: The Lost City Of Heracleion

Before its discovery in 2000, the ancient city of Haracleion was nothing but a passing mention in a few rare inscriptions and ancient texts, according to The Guardian. Archaeologist Frank Goddio spent years searching for the real lost city, which he knew to be off the coast of Egypt.

Using advanced underwater screening technology, he finally found it submerged 6.5 kilometres off the coast. Among the ruins were 64 ships, 700 anchors, gold coins, and statues standing 16 feet tall.

17 15. Underwater: The Undersea River In The Black Sea

In 2016, researchers working in the Black Sea discovered currents of water flowing along the seabed that were 350 times greater than the River Thames.

Using an underwater robot to study the river, scientists from Leeds University found that the river had carved out deep channels, much like a river on land. It was even 115ft deep in places, and had rapids and waterfalls.

Placed on the land, this river would rank sixth in the world for the volume of water that flows through it.

16 24. Underwater: The Stonehenge In Lake Michigan

Of all the things lurking in the middle of Lake Michigan, an aquatic Stonehenge wouldn’t be the first thing to spring to mind. But in 2007, Mark Holley, professor of underwater archeology at Northwestern Michigan College, discovered a strange series of stones 40 feet below the lake’s surface, mysteriously arranged in a circle.

Even more exciting, one stone appeared to be engraved with what looks like the image of a mastodon, an elephant-like animal that went extinct about 10,000 years ago, according to NBC Chicago. Without further excavation, however, the site has remained a mystery.

15 23. Underwater: New Jersey's Train Graveyard

Off the coast of New Jersey, archaeologists found two rare, well-preserved steam trains under 90 feet of water. The locomotives are from the 1850s and no-one is entirely sure how they ended up at the bottom of the ocean, according to the Daily Mail.

There’s no record of the trains being built or lost, although it’s likely they were being transported by barge when a storm hit, forcing the crew to push them overboard to prevent the boat capsizing.

14 22. Underwater: An Ancient Greek Computer

Discovered by divers in 1901, it took the best part of a century for scientists to figure out exactly what the Antikythera Mechanism was for. As it turns out, it’s an ancient Greek analogue computer.

Thanks to x-ray technology, scientists have solved the puzzle of the device, which is about the size of a mantel clock. It was used a sophisticated calendar and computer, mapping the solar and lunar calendars, according to the Smithsonian Magazine. It could even count down the days until the next Olympic Games.

13 13. Underwater: The Mariana Trench

The Mariana Trench is the deepest part of the Earth’s oceans. Estimates vary, but at its depths, it’s 6.8 miles deep, and it’s five times longer than the Grand Canyon.

The trench was first sounded in 1875, using a weighted rope, but the first descent wasn’t attempted until 1960. There have been three more since, most recently in 2012 by Canadian film director James Cameron. He reached the bottom of the trench in the submersible vessel Deepsea Challenger.

The trench is one of the most mysterious locations on the planet, with so little known about it, and it's also home to some of the most bizarre creatures on the planet.

12 12. Underwater: The 2,400-Year-Old Boat In The Black Sea

In 2018, archaeologists made an incredible discovery more than a mile below the surface of the Black Sea off of the Bulgarian coast - the world’s oldest intact shipwreck.

The incredibly well-preserved boat is estimated to be around 2,400 years old, according to The Guardian. The ancient Greek vessel is 23 metres long and a lack of oxygen at the sea depth has meant its mast, rudders, rowing benches and other details, are all perfectly intact.

11 11. Underwater: £150 Million Of Lost Silver

The US deep-sea exploration company Odyssey Marine discovered the SS Gairsoppa in 2011. The cargo ship had been torpedoed by a German U-boat off the coast of Ireland in 1941 when it was returning home from India, while in the service of the British Ministry of War Transport.

So far, more than 200 tonnes of silver, worth a staggering £150m, has been removed from the ship, according to the BBC. Odyssey Marine will get to keep 80 percent of the haul after expenses and the remaining 20 percent will go to the British Treasury.

10 10. Ashore: Thousands Of Snowballs In Siberia

It might be a natural phenomenon, but it still took villagers near the Gulf of Ob in Siberia by surprise when they discovered scores of snowballs lining the shore.

According to Live Science, in 2016 an 11-mile stretch of beach was covered in balls ranging from the size of a tennis ball to a massive three-feet in diameter. The spheres are shaped by the winds and movement of the tides and only occur only in the right conditions.

9 9. Ashore: Love Letters From WWII

In 2012, New Jersey resident Kathleen Chaney discovered a stack of 57 love letters, bound with a pink ribbon and nestled inside a box, on the shore of Sandy Hook Bay, just a day after Hurricane Sandy.

This incredible find was the correspondence between sweethearts Dorothy Fallon and Lynn Farnham and was written between 1942 and 1947. Chaney tried to return the letters to their rightful owners, but was only able to track down the couple’s niece, according to NBC New York.

8 8. Ashore: Giant Lego Man Washes Up In Japan

The fact an eight-foot-tall lego figurine has washed up on any beach, anywhere, is weird enough. The fact such an object has come ashore on beaches on the Netherlands, UK, Florida and Japan, is downright bizarre.

But it’s no coincidence. It’s actually the work of an artist who goes by the name of Ego Leonard and the giant Lego figures are kind of his signature thing. Each Lego man has “No Real Than You Are” written on its t-shirt, which adds a whole new layer of trippy.

7 7. Ashore: A 65-Year-Old Plane In Wales

A US fighter plane from WWII, known as the Maid Of Harlech, crashed off the coast of Wales in September 1942. The pilot survived but the plane wasn’t seen again until it washed ashore in 2007.

According to Wales Online, the exact location of the Lockheed P-38 Lightning fighter aircraft remains confidential, to protect the plane. Its weapons have been removed but the plane still remains on the sand today, just waiting to surprise dog walkers and beach-goers.

6 6. Ashore: Nearly 100 WWII Bombs

Back in 2011, residents of Hampshire got a bit of a shock when 87 unexploded WWII bombs washed up on Calshot beach. The mortars measured about 10cm by 50cm, according to the BBC, and were dealt with by a five-man team bomb disposal team from the Royal Navy, who carried out controlled explosions on the devices.

There was some speculation that the so-called Supermoon the previous week was partly responsible for exposing the bombs, because it created very low tides. Alternatively, it’s possible fishing nets had pulled them up.