Minecraft wiki entry for Defeating_a_monument, associated text: After that is done you can simply raid the monument of its sea lanterns, sponges, prismarine, and gold and leave. Alternatively, you can turn it into a base or a guardian farm. Now that Mining Fatigue is no longer an issue, you can use any method you'd like to accomplish this. If you were lucky enough to find a sponge room (or three), the sponges will be particularly helpful in this task, as the sponges will soak up a lot of the water. Even if you did not find a sponge room, you can use the sponges from the elder guardians, or previously-obtained sponges from other monuments.