A nether fortress, also just called a fortress, is a large and complex structure that mostly consists of bridges, corridors, and towers. This structure can only be found in the nether.
A nether fortress (via screenshot)
Introduced to the game in pre-release Java Edition beta 1.9, nether fortresses were built out of nether brick, nether brick fence, and nether brick stairs. They are one of the only two places where nether warts can be naturally found.
Nether fortresses can be found in all nether biomes. The game splits the nether into sections or regions, and these regions dictate whether a fortress can spawn in them. These regions are usually 432x432 blocks in Java Edition and 480x480 blocks in Bedrock Edition.
There is a buffer zone of 4 chunks which are on the south and east borders of these zones. Since this buffer zone does not add to the region size, it makes the sections in Java Edition 368x368 blocks and Bedrock Edition 416x416 blocks. Two structures cannot spawn in the same region, however they can overlap if they generate close to the borders of two regions.
There are different chances for nether fortresses to generate in Java and Bedrock Editions, they are 40% and 33.3% respectively. Sometimes a nether fortress can be buried in netherrack in such a case the interior will not be blocked off by nether racks, and the hallways and corridors will be clear and traversable. It is also possible for crimson trees, glowstone, and warped trees to spawn inside the fortress.
Nether fortresses are large structures high above the lava seas and are supported by massive pillars made of nether brick materials. When a fortress is generated, a four-way crossing at coordinates 11,~11 of the designated chunk is first generated. The two areas of the fortress consist of exterior and interior areas. The exterior areas can go through netherrack and give a tunnel feel.
The exterior areas usually consist of:
A long exterior bridge (via screenshot)
The interior structures have windows (1x2 size) that have nether brick fences as window panes. The rooms that are found in the interior include:
An interior room with a staircase (via screenshot)
Nether fortresses have a list of possible mob spawns that are different from the list used for the rest of the nether. Regardless of the biome, the fortress will generate mobs only from this list alone. This includes skeletons, magma cubes, and zombified piglins as well as two mobs that are exclusive to the fortress: blazes and wither skeletons. The spawning algorithm will check for two requirements:
Wither skeletons, zombified piglins, and a blaze on a nether bridge (via screenshot)
If both the requirement checks pass, the game will use the special mobs' list that is for nether fortresses instead of the default biome list when choosing what mobs to spawn. The actual process of spawning the mobs proceeds as normal for the mobs chosen for the list.
The chests that can be found across the nether fortress have a preset loot pool from which to spawn items:
Nether fortress is filled with items and mobs for the players to loot and kill. They can be quite hard to navigate. They are cool and well-built structures that add to the character and environment of the nether and help in making the experience more immersive.
A. Nether fortresses can spawn in any biome in the nether.
A. The mobs that spawn in the fortress are Blazes, Magma cubes, Skeletons, Wither skeletons, Zombified piglins, and Zombified chicken jockeys.
A. Nether fortresses have a 40% chance and 33.3% chance of generating in the Java and Bedrock editions, respectively.