How to Find an Ocean Monument in Minecraft

Guide Java Bedrock

Quick answer: Ocean monuments generate in deep ocean biomes, at most one per 512x512 block area. Look for an ocean explorer map offered by a cartographer: its structure icon marks a monument, which is not necessarily the closest one to you.

What you need

Ocean explorer map (or a boat)
Water breathing + night vision potions
Milk buckets for Mining Fatigue

Step by step

Check a cartographer for an ocean explorer map. If that villager does not offer one, try another cartographer. Follow the monument icon on the map; do not assume it points to the monument closest to your current location.
Or sail the deep oceans: monuments only generate in deep ocean biome variants (deep ocean, deep lukewarm, deep cold, deep frozen). A boat, night vision potions and a high vantage point help you spot the prismarine silhouette glowing with sea lanterns.
Or use commands: /locate structure minecraft:ocean_monument prints the nearest coordinates.
Know the spacing: at most one monument generates per 512x512 block area, so if you find none in one ocean, keep sailing - every deep ocean region has its shot.
Prepare for the dive: water breathing potions (8 minutes), night vision, good armor, a sword or trident, food, and doors or other air-pocket blocks if you play Java. Milk buckets cure Mining Fatigue.
Expect Mining Fatigue III from elder guardians within 50 blocks. It lasts 5 minutes. Kill all three to prevent new applications; milk clears the current effect, but Bedrock elders can reapply it immediately while you remain in range.
Kill the three elder guardians: one in the top room and one in each wing. Killing one yourself gives a wet sponge, plus chances for prismarine loot and a tide armor trim.
Loot the monument: the central treasure chamber hides 8 gold blocks inside dark prismarine. If sponge rooms generated, each holds about 30 wet sponges. Some monuments have no sponge rooms.
For a guardian farm, choose a design for your edition. Bedrock guardians use 25 fixed spawning columns associated with the monument; a Java farm layout should not be assumed to work in Bedrock.

Java vs Bedrock

Guardian spawning and farm layouts differ between editions: Bedrock uses 25 fixed spawning columns. Java elders check for Mining Fatigue once per minute; Bedrock elders afflict players without the effect immediately in range. Doors provide underwater air pockets in Java, but waterlog in Bedrock.

Versions: Describes the current Java and Bedrock releases. See the edition note above for differences.

Frequently asked questions

Where do ocean monuments spawn in Minecraft?

In deep ocean biome variants, at most one per 512x512 block area. A cartographer may offer an ocean explorer map marking a monument, or you can use /locate structure minecraft:ocean_monument with commands enabled.

How do you get rid of Mining Fatigue from an elder guardian?

Milk clears the current effect. Kill all three elders to prevent reapplication, then drink milk or wait for the effect to expire. In Java they check once per minute; in Bedrock they can reapply it immediately while you are in range.

What loot is in an ocean monument?

8 gold blocks in the central treasure chamber, prismarine and sea lanterns, plus about 30 wet sponges per sponge room if any generated. Killing elders yourself gives wet sponges and a chance for tide armor trims.

Do guardian farms work the same in Java and Bedrock?

No. Use an edition-specific design. In Bedrock, guardians spawn in 25 fixed columns associated with the monument, and removing the building does not remove those spawning locations.