Minecraft wiki entry for Defense, associated text: Ghasts cannot see through glass, so if you are in the Nether with some glass, you could make a glass box around yourself to defend yourself. This is helpful because you can see when the danger of a ghast has gone. Building a glass base around your Portal in the Nether is a good idea, because you will be able to see the nether's epic terrain, and still be protected from ghasts. Ghasts also can't see through sugar cane or vines; however, sugarcane is impossible to plant in the Nether normally, due to the fact that you can't get water into the Nether without using commands (such as /setblock. Keep in mind that ghast fireballs have low blast penetration, so many materials are ghast-proof (cobblestone being the best known). This doesn't apply to netherrack (which is extremely weak) or any of the transparent blocks. It is traditional (due to Mojang suggesting it to players constantly on the Xbox version) to build a cobblestone room around the nether portal to protect it. Also, since ghast fireballs can put out an unprotected portal, always bring a flint and steel with you. Note that a ghast fireball can also relight an unlit portal, but only if the fireball itself lands in the frame (rather than with its area effect).