Minecraft wiki entry for Superflat_survival, associated text: Before venturing to the Nether, make sure the player has a diamond sword, a full suit of armor (preferably iron or diamond), and of course, at least 10 obsidian. If you have 10 obsidian, you need 4 other blocks to use as placeholders, because you can't place blocks on the corners or edges of other blocks. It's also a good idea to make an enchantment table before the portal, as enchantments greatly help the player in the Nether.