Minecraft wiki entry for Surviving_in_a_single_area_indefinitely, associated text: One of the hardest parts of SkyBlock is finding a nether fortress. This is because SkyBlock only consists of a few blocks, which is not enough room for a nether fortress. However, mobs that only spawn in nether fortresses will spawn where a nether fortress would be if it were a normal map. One way to do this is to keep building platforms outwards, until nether fortress mobs start spawning. Note that this may take a very long time, as nether fortresses are often very far away from each other. Another way how to find a place where nether fortress mobs should spawn is to find seed of your skyblock world using /seed and then create a normal world, using the seed. Then enter the nether portal, find nether fortress, memorize the coordinates of it and then build a platform at the skyblock world exactly on these coordinates.