Minecraft wiki entry for Best_biomes_for_homes, associated text: As an opposite to the sky, the underground may require the player to spend lots of time mining out space for structures. Any room or cave near the player's base will need to be lit up sufficiently to prevent mob spawning, however, a wandering trader along with two trader llamas can also spawn underground. However, the player would be living right next to a vast amount of resources such as iron, diamond, and more. While likely less desirable than living on the surface, living in the underground can provide a unique survival experience.