Minecraft wiki entry for Spawn, associated text: Structure spawn attempts occur at specific relative X and Z coordinates in naturally generated structures, known as "hard-coded spawn spots". The structures that have hard-coded spawn spots include swamp huts, ocean monuments, pillager outposts, and nether fortresses. Whenever a successful cluster spawn attempt occurs within a chunk that contains a hard-coded spawn spot, the environmental spawning algorithm also attempts a structure spawn. (Note that a "successful attempt" here means that a spawnable block was found, even if the spawn was then blocked by light level check or mob cap check.) The structure spawn attempt follows the same rules and steps described above for cluster spawning, with the following changes: