This is something that was custom made on my server for the Demon Spawn. For those who do not know, the server uses a custom plugin called Supernatural Classes, and one of which is a Demon class which resides exclusively in the nether. No lava, fire, magma block, etc. damage, and friendly to most nether mobs. As such, we're creating a sanctuary town for those Demons. The image listed is the Black Smithing building.