The Ocean is a large, deep body of water that spawns at both ends of a world.
You can tell that you are close to the Ocean when the background changes to sparse green mountains that appear to be mostly submerged in water. Oceans will always reach the end of the map (though usually not past it).
When you reach the Ocean proper, the ground will almost always change to sand (though, unlike Deserts, there will not necessarily be Cacti) and will rapidly drop off into water. Any submerged sand blocks may have Coral growing on them.
Mobs exclusive to the Ocean include Pink Jellyfish, Crabs, and Sharks. Orcas can also spawn, but only in the Console Version. Oceans are also far enough away from spawn that it is possible for Goblin Scouts to appear in or around them, as well.
Through experimentation, it has been determined that it is possible to create a fully functional artificial ocean. For an area to be considered an ocean, it must meet the following requirements:
- Have a floor of sand at least one block thick.
- At least one block of water.
- Must be at least 1/3 of the way from spawn. [confirmation on distance?]
- The same music theme is used for both Forest and Ocean.
- The Coral that grows on the Ocean floor is key to traversing this biome with minimal effort, as it can be used to make Gills Potions.
- Creating an air tunnel along the floor of the ocean is an easy way to make your way across, but it is very tedious work. Further exploration and experimentation has shown that should you make a Hellevator in this air tunnel and dig a hole through your tunnel, the ocean will pour through. When the first bit of water hits the Underworld, the water evaporates (as of 1.0.5). When this happens, all water that is falling and would eventually fall to The Underworld instantly disappears, leaving only what ocean water would remain (water that didn't have an open path to fall through). This proves that the ocean is not infinite and can be removed from your world if you wish to do so.
- Drained Oceans are treated as Deserts, including spawning all of the appropriate monsters. In Hard Mode, they can even become Corrupted or Hallowed.
- Corrupted Oceans will not spawn Sharks.
- On rare occasions the map stops but allows you to go on, thus being able to travel to the underworld without digging.
- Occasionally, the water on the very edge of the map may become "stuck", and will only be viewable with third party tools.