Nether fortresses are castle-like structures in the Nether. They are made of Nether brick and/or Netherrack  and are home to blazes and wither skeletons. In them, you may find soul sand and Nether Warts. Occasionally, there will be lava blocking the player's path. They contain chests with various types of items. The castle-like building also consists of blaze spawners. The Fortress sometimes spawns weird and is full of glowstone and/or netherack.


A blaze spawner


A blaze

Nether Brick

Nether fortresses are almost completely made of nether bricks