Nether Fortress

A Nether fortress is an uncommon large structure made of Nether bricks found in the Nether, consisting of bridges, corridors, and towers. Nether fortresses are the only place where wither skeletons and blazes spawn. They also contain Nether wart.

Nether fortresses generate in all Nether biomes. To do so, the game splits the Nether into regions in which one of either a fortress or a bastion remnant can generate. The regions are 432×432 blocks in Java Edition and 480×480 blocks in Bedrock Edition.

Each region has a four chunk separation located on the south and east borders of the region in which neither a fortress nor a bastion can generate.