Minecraft wiki entry for Underwater_home, associated text: You can make an ocean monument your underwater base. After Raiding an ocean monument, you can make it your underwater base. First, see Tutorials/Defeating a monument for advice on how to defeat the monument. After you have removed the threats, separate each room by using blocks or doors. After that, use sponges to clear out the water in the room. Finally, repeat doing this to each room until you have a whole ocean monument with no water inside. If you need to, you can also clear the water outside, so no guardians spawn outside of the monument. You can build conduits to give conduit power to players. You may break the walls inside the monument too.