Ocean Monument

Ocean Monuments are naturally generated structures that appear in Deep Oceans, sometimes intruding into nearby regular Oceans. Monuments are inhabited by Guardians and three Elder Guardians.

Spawning
Ocean monuments can only spawn in areas where it has a Deep Ocean biome at its center point. It requires an aquatic biome (regular/Deep/Frozen Ocean, regular/Frozen River) everywhere within a 29 block square radius around the center point.

Ocean Monuments can spawn in existing chunks from older versions of Minecraft.

Structure


The monument is constructed entirely from variants of Prismarine and lit by Sea Lanterns. It includes a large central section flanked between two wings. Under the monument are 23 giant pillars that stretch to the ocean floor. The main entrance is located at the front of the central section.



The central section consists of various types of chambers. The chambers are randomly generated; each monument has a different number of rooms (at least six) arranged in a unique manner. The chambers connect vertically and horizontally to the different parts of the monument, including the left and right wings. Near the center of the central section is the treasure chamber, a tall room with eight gold blocks encased in Dark Prismarine. At the topmost room resides an Elder Guardian.

About half of all monuments contain a room with wet sponges on the ceiling. Sometimes, though rare, a monument can contain multiple rooms with Wet Sponges.

The two wings can be switched in each monument. One of the wings contain a large room with a small pillar at the center. The room contains a second Elder Guardian. The other wing is a huge open space with a large, square-shaped platform. It contains another Elder Guardian. A long hallway that arcs around the wings and the back portion of the monument connects the two wings together.

Ocean Monuments will always contain three Elder Guardians - one at the top and one in each wing.

Strategy


The difficulty of the dungeon is largely dependent on the player's preparations. The primary threat when taking down the monument is drowning, but this is easily prevented using a potion of Water Breathing, or a Respiration enchantment. The amount of potions of Water Breathing the player should bring is determined by how long the player will stay underwater. If you should happen to run out of potions of Water Breathing, you can place a Torch on a wall right next to you. Despite the surrounding water, the torch will stay put just long enough to form a pocket of air you can use to refresh your oxygen meter. You can also use Glass Panes, Iron Bars, Ladder, or Fences to create a permanent pocket of air. The next main threat is the dangerous Guardians. Due to this mob's high health, fast movements, and a powerful ranged attack, players with weak armor and swords will be quickly overrun by the large groups of Guardians surrounding the structure. Strong enchanted armor is recommended when combating the mobs. Swords are the preferred method of combat, since bows are ineffective underwater. Potions of Invisibility can also be used to avoid most Guardian attacks. When approaching the monument, a ghostly image of an Elder Guardian will appear in the screen and the player will be inflicted with Mining Fatigue III. This effect is inflicted by the Elder Guardians, and not from the monument. Due to the effect, breaking through walls will be nearly impossible until all Elder Guardians are killed. Thus, the player is forced to enter through the main entrance and explore through the rooms to find all three Elder Guardians before otherwise. Milk buckets can help negate the effect, but only for a short moment.

Once inside, the player will meet with a severe lack of visibility and mobility, due to being underwater. This can be resolved with Potions of Night Vision, the Respiration enchantment for visibility, and a Depth Strider enchantment for mobility. Because each monument has differently generated rooms, exploring the structure can be quite confusing. Blocks can be used to keep track of rooms that have already been visited, but keep in mind that the Mining Fatigue will make it difficult to reclaim them. See above for more details on the structure of the monument.

Battling Guardians will be more or less troublesome because of the lack of space in most rooms. If the player is well armored, Guardians should be a mere disturbance when exploring. Elder Guardians contain very high health and damage, but its large body hinders its movement, allowing players to quickly dispatch them if they are equipped with strong swords. Once all Elder Guardians are defeated and the effect wears out, the player can freely roam the monument and mine out any valuable blocks. If the player prepares thoroughly, and carefully observes remaining potion time, completing the monument will run rather smoothly.

After Beating the Dungeon
Ocean monuments continue to be a valuable resource even after looting the gold and taking the Elder Guardian's drops. They are the only spaces that allow the spawning of Guardians, and therefore are the only places that large underwater Prismarine grinders can be developed. The structures themselves can be turned into complex underwater bases, using the mechanics of sponges to clear out the water inside.

Using sponges to clear out underwater structures is difficult, and should be done like this: clear out the water near the roof first, and work your way down. If you start near the floor, water from the roof will simply cascade down into the opening you just made. Any "bleeding" of the sponge's area of effect into the outside will quickly be taken care of by the surrounding water.

Trivia

 * The base area of the monument is 58×58 blocks, which is significantly larger than Desert Temples (21×21) and Jungle Temples (15×12). It is slightly smaller than the average Stronghold, however.
 * The structure actually generates containing water as part of the structure. This is likely to ensure that there are no air pockets formed inside.