Minecraft wiki entry for Multiplayer_PvP_bases, associated text: Penetrating the top bedrock of the Nether will give you a very large, flat plain of bedrock(with the occasional mushroom) to work with. Also, as the top of the nether can only be penetrated by the most skilled players, stealth is completely optional. Build a normal, overworld above-land stronghold on top of this bedrock and light up your area (mobs usually won't spawn on bedrock, but they'll start appearing once you start building something else). If possible, elevate the base 1 block from the bedrock surface so that anyone attempting to pop above the bedrock directly under your base will succeed (and suffocate), and use a Fire Resistance potion and lava to build TNT-proof walls. Exit can usually be achieved with a Nether portal or /spawn. One can also build a nether-sky base once they get up the bedrock.