How does one make an efficient kill room in Minecraft, that can survive creeper explosions?
So, I contained the spawner; I can probably augment it with some spawn rooms that will transport the mobs to the shafts dropping them the needed 22 blocks down to what is to be the room where I kill them. Then I'll have a creeper blow up and set all consecutive survivors free.
I know the walls must be built from obsidian, but how do I make the gap in it to swing my sword through? The text tutorials are rather sketchy, and the video tutorials use either fenceposts (which are definitely not blast proof) or some kind of transparent grid which I failed to identify (a different tileset, maybe?).