Obsidian Back Wall

Obsidian Back Wall is an unobtainable background wall found in the cavern below the same elevation point as lava. They can be destroyed using a Hammer or Hamaxe, though they drop nothing. These naturally occurring walls will not stop enemies from spawning and are not suitable for housing.

As of 1.4.01 an identical version that stops enemies from spawning and is suitable for housing can be crafted with ecto mist