Minecraft wiki entry for Shelters, associated text: Once you have at least 10 obsidian, either from mining it in a cavern or obtaining it through obsidian farming you can build a nether portal. Once built, activate it with a flint and steel, and you can travel to the the Nether. This can be used for fast travel and for getting lava, netherrack, Soul Sand, Nether quartz ore and glowstone. Beware of ghasts, zombie pigmen and blazes as well as magma cubes. Building another nether portal room in the nether for protection is a recommended idea. Please note cobblestone is a good block to build with in the Nether since ghasts can't destroy it with their fireballs.