Ocean

The Ocean is an area found on the surface of each map. It buffers the very ends of the map, comprising the eastern 500ft (250 blocks) and the western 500ft of the map that lie above the Cavern Layer depth.

It is a large body of water which gets very deep before hitting the invisible wall at the edge of the map. Coral can be found underwater. If players without proper accessories try to swim to the side of the map, there is a serious risk of drowning. It is recommended to bring a Breathing Reed, a Magic Mirror and/or Flippers, but not quite necessary. At the very least have a Grappling Hook and a few Healing Potions.

Oceans will commonly contain chests with loot pertaining to water.

Enemies
Shark, Jellyfish and Crab.

Chest running
A very popular technique is to generate a SMALL or MEDIUM sized map. Then using the Necro Armor, Hermes Boots, Anklet of the Wind and other speed boost items, the player would run from one side of the map to the other. Since there is a very good chance to have some Chests in the ocean, it is a very popular technique to get medium-tier items. The chests will usually contain items such as Breathing reeds, Shurikens, Magic Mirrors, Dynamite and Coins. Even behind the Dungeon there is an ocean, so it is advised to have a Grappling Hook. A Magic Mirror would also be helpful, so that you don't need to run all the way back.