Minecraft wiki entry for Defeating_a_Nether_fortress, associated text: Nether fortresses are large structures found in the Nether. Exploring them is essential to game progression, as they are the only places you can find blaze rods and wither skeleton skulls, and one of the two places where nether wart is found. Be careful, however, because these structures are huge and you can easily get lost/killed by powerful mobs.