Nether Fortress

Nether Fortresses are Generated Structures that spawn in the Nether dimension, which was added in Update 0.12.1. They are very dangerous due to their Blazes and Wither Skeletons.

They are large structures consisting of Nether Brick Blocks, Nether Brick Stairs, and Nether Brick Fences. They also contain loot-filled chests, Blaze Spawners, Wither Skeletons, and, most of the time, 2x5 areas of Soul Sand with Nether Wart.

Structure
Nether Fortresses have a complicated structure with various rooms, including:
 * Lava Well Rooms.
 * Rooms with Nether Brick Stairs in the center, and Soul Sand at the sides of the stairway containing two 2×5 rows of Nether Wart growing on it.
 * Rooms with Blaze Spawners, which can have Nether Brick Stairs leading up to them, also have Nether Brick Fences.
 * Rooms with four exits. Some of them lead only to the outside.
 * Rooms with a "stairway" of Nether Brick placed against a wall, leading up to the floor above.

Trivia

 * Some Nether Fortresses have no growing room, so you won't find any Nether Wart in them.
 * There is a 20% chance that a regular Skeleton will spawn instead of a Wither Skeleton.
 * Zombie Pigmen can also spawn in Nether Fortresses, along with the other dangerous Mobs.
 * This is one of the biggest generated structures, like the Stronghold.