Water covers the majority of the planet, so it's no surprise that there are some incredible sights hidden under the surface of the world's oceans. There are curious seals, giant whales and giant jellyfish, all adding to the spectacular nature of the sea.
We've put together a selection of some of the best underwater images showing the deep blue in all its glory – you won't want to look away.
1. What’s the sting like on that one?
The waters around the remote and uninhabited island of Sula Sgeir, Scotland were where this giant jelly was photographed.
2. A curious seal
It was time to strike a pose for this grey seal swimming in the North Sea, off the English coast.
3. A deep dark cave
It looks bright enough to see in this cave, but that's just thanks to the photographer's skills. The photo was taken in the inky blackness of the Weebubbie Cave, Australia and the image was part of Red Bull Illume 2013. The international photography contest dedicated to action and adventure sports is back for 2016 and submissions are now open.
4. Wonders of the ocean
A diver swims with a small lion's mane jellyfish near an iceberg in the Tasillaq Fjord, East Greenland.
5. Giants of the sea
Freedivers Alex Voyer and Alex Roubaud spent time in the Indian Ocean and captured some incredible images of sperm whales. See more from their trip.
6. The fight for food
This image shows nature at its best as a group of northern gannets fight over fish in Scotland.
7. Big fish, little diver
This picture, shot at a great angle, shows a diver and sunfish in Bali.
8. Underwater interaction
A diver and dolphin check out a jellyfish in this image shot while freediving in Ireland. It was also part of Red Bull Illume.
9. Dancing with a whale
A freediver dances with a sperm whale in this shot, also taken in the Indian Ocean.
10. A singing shark
This whale shark gives its lungs a blast in the Mexican waters.
11. Freediving with a seal
Check out this beautiful moment when a seal notices the freediver swimming gracefully behind.
12. A mesmerising turtle
This green turtle was pictured swimming in the Marsa Shouna dive site in the Red Sea, Egypt.
13. Watch out for the shoal
A diver looks on at a huge shoal of fish swarming in the waters off Koh Pha Ngan, Thailand.