Well, as of today, the next adaptation of the Chronicles of Narnia series (the Voyage of the Dawn Treader) is now in theaters. One of C.S. Lewis's popular stories, it follows the adventures of Edmund, Lucy, and their practical cousin Eustace as they journey across Narnia's oceans to find Aslan's Country. This book explores a part of Narnia that, like our oceans, are deep and mysterious. In fact, so little is known about our oceans and what lies underneath them that people have been trying to figure that out for years.
One of the earliest tales of a sailor exploring the oceans goes back to Ancient Greece, in Homer's epic tale The Odyssey. The hero, Odysseus (known as Ulysses in Rome), has helped Greece win the Trojan war, but a series of events leads him to take 20 years to get home. Along the way, he encounters man-eating cyclopes, deadly enchanting sirens, and the infamous Scylla and Charybdis. These adventures are referenced in The Voyage of the Dawn Treader, showing that the author was familiar with tales from Ancient Greece.
The Norse also had tales of sea creatures lurking in the deep. The most famous of these creatures was the Kraken, a giant octopus/squid like creature that pulled ships down to the bottom of the sea. What's scary is that the legend of the Kraken may have actually been a real creature! Although they don't pull ships down to the bottom of the sea, there is evidence that giant squid live in the oceans. Remains of giant squid have even been found in the stomachs of sperm whales, showing that if provoked they can be aggressive!
One of the most famous monsters to be seen in the oceans are sea serpents. For hundreds of years sailors have told stories of large, snake-like creatures that swam in the oceans. No reports of destroying ships are known, but that doesn't mean they were capable of doing so. They can easily be seen as the ocean's equivalent of the dragon, except that they didn't breathe fire or eat anyone (even though they could easily eat a ship if they wanted to).
Another famous sea creature that probably everyone is familiar with is the mermaid. These are some of the most unusual creatures around, because they were half fish, half women (more recent stories added male versions as well). The early stories had them behave like sirens, using songs to lure sailors to their deaths. More recent stories just have them as sea dwellers who love to sing. Perhaps the most famous story featuring mermaids is Hans Christian Anderson's The Little Mermaid, which became Disney's 28th animated film. Tales of mermaids have withstood the test of time, and it's quite safe to assume that they will still exist in fantasy stories for years to come.
While people had many stories about creatures hiding in the deep oceans, there is evidence that shows that long ago, the oceans were filled with monsters. Throughout history, super predators have evolved in the oceans of the world. In the Devonian era, the oceans were ruled by a monstrous fish-like creature known as Dunkleosteus, a fish with a bite so nasty a person would lose their leg completely from it. Later, in the age of the dinosaurs, creatures like Elasmosaurus (a long-necked plesiosaurus), Liopleurodon (a huge short-neck pliosaur the size of a whale), and Mosasaurus (a crocodile-like creature with flippers) ruled the oceans. After the dinosaurs came the whales, but these were killers like Basilosaurus, nothing like the gentle giants of today.
Perhaps the most ferocious sea creature was the real life Jaws: Megalodon. Megalodon was a 50-foot shark that swam in the oceans about 25 to 1.5 million years ago. This shark was capable of eating whatever it wanted. No doubt the great whites of today would seem like harmless guppies compared to this creature. If it were still alive, nothing would be left of the surfers who'd probably get attacked.
The oceans are a vast and mysterious place. Writers and movie makers have been telling stories that explore these vast realms (like Jules Verne's 20,000 Leagues Under the Sea and Disney/Pixar's film Finding Nemo). With the way research technology has advanced, we may find more discoveries under the sea that we had no idea existed or were possible.