Minecraft wiki entry for Defeating_the_wither, associated text: Dig out a 5x5x2 hole underneath the bedrock of the end portal. Make sure to leave a staircase to exit easily. Replace the exact center 3x3 area 3 blocks underneath the bedrock with obsidian. This is very important, as if it is not the exact center of where the portal is, the wither can escape the portal and start blasting the endermen. Place soul sand on top of the center obsidian block, and place three more soul sand on any side of the obsidian. Place three wither skulls on the side of the 3 soul sand, and the wither will spawn. Run away to avoid the explosion. After the explosion, you can simply run back and hit the wither with your sword. The wither will be unable to hit you back.