Ocean Monument

"Dive into the deep blue and you may see them shimmering through the hazy water: sprawling pyramidal structures built by unknown hands, but still patrolled by spiny Guardians - spheroid, cyclopean fish-beasts."

- Marsh Davies

Ocean monuments, or simply monuments, are rare underwater structures found in deep oceans biome and variants. They are inhabited by guardians and elder guardians. They are the only place where sponges can be found and one of the only places where prismarine can be found; the other being ocean ruins.

Generation
Ocean monuments generate in areas with deep ocean biome variants everywhere within a 16 block square radius around the 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 generates around the monument as a part of the structure.

Ocean monuments can generate in existing chunks from older versions (1.7 or later when deep water biomes were added although they have been also noted in worlds generated in older versions) of Minecraft, as long as players have not spent more than 3 minutes total near those chunks.

They can be located with ocean explorer maps, which are bought from cartographer villagers with emeralds.

Structure


The monument is constructed entirely from variants of prismarine and lit by sea lanterns. It includes a large central section flanked by 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 base size of the structure is 58 × 58 blocks.

The area of the ocean monument spawns only guardians after generating, also being the only location they spawn. $$ all hostile mobs can spawn in areas of the monument that are cleared of water.



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. Sometimes, these rooms can come in multitudes. It's possible for a monument to generate without sponges.

One of the wings contains a large room with a small pillar at the center. The room contains a second elder guardian. 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 always contain three elder guardians - one at the top and one in each wing.

Trivia

 * Ocean monuments generate normally in customized worlds with lava oceans set to yes, and some water patches appear in the lava that shield themselves with obsidian if updated.
 * Guardians and drowned are the only hostile mobs able to spawn within the 58×58×23 area containing the monument; normal Overworld hostile mobs do not spawn inside.
 * Icebergs may generate on monuments, making elder guardians suffocate in icebergs.