Minecraft wiki entry for Multiplayer_PvP_bases, associated text: Dig a hole down to where you want your base to be. Have people guard the top of the hole. When you reach the void, use lava and water to build a cobblestone pillar to the void. Place ladders on the cobblestone. At the bottom, make an overhang and use that to start your base. Fill in the deep hole so raiders cannot get in. Use a flying machine/elytra for leaving the base or going to the surface.