Ocean Monument

Ocean monuments are naturally generated underwater structures that appear in deep oceans. They are inhabited by guardians and elder guardians.

Generation
Ocean monuments only generate in areas with a deep ocean biome at its center point, and an aquatic biome (regular/deep/frozen ocean, regular/frozen river) everywhere within a 29 block square radius around the center point. In order to prevent air pockets, water will generate around the monument as a part of the structure.

Ocean monuments can spawn in existing chunks from older versions of Minecraft, as long as players have not spent more than 3 minutes total near those chunks.

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. At the topmost room resides an elder guardian. Around the center of the central section lies the treasure chamber, a tall room with eight gold blocks encased in dark prismarine.

Occasionally, monuments contain a room with several wet sponges on the ceiling. Rarely, these rooms can come in multitudes.

One of the wings contains a large room with a small pillar at the center. The room contains a second elder. The other wing is made up of a huge open space with a large, square-shaped platform, containing 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.

After beating the monument
Ocean monuments continue to be a valuable resource even after looting the gold blocks and taking the elder guardian drops. They are the only spaces that allow guardian spawnage, 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.

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). However, it is slightly smaller than the average stronghold.
 * Ocean monuments generate normally in customized worlds with lava oceans set to yes, and some water patches will appear in the lava which will shield themself with obsidian if updated.
 * Guardians are the only hostile mobs able to spawn within the 58×58×23 area containing the monument; normal Overworld hostile mobs will not spawn inside.