Biome backgrounds are images that appear behind objects and blocks in each biome. A few of the Calamity Mod's biomes have unique backgrounds that usually show a landscape of the biome. Backgrounds do not affect a biome in any way. Turning off backgrounds in Settings hides them, though ambient objects will still appear.

It crash-lands into the Dungeonside of the world via a meteor upon defeating the Wall of Flesh, which infects the nearby terrain and extends somewhat deep underground. The biome is filled with a sickly purple haze, and is populated by many alien creatures as well as dark monoliths of various sizes.