Minecraft wiki entry for Trapdoor_uses, associated text: You can create a fairly good drawbridge; You can extend it lengthways and its widthways. It's possible to walk on the ledge of an opened trapdoor if there is enough space above it. To create a drawbridge in this fashion that is not vulnerable to ledge walking, so long as there is an overhang 2 blocks above the ground before the trapdoors start. Trapdoors can also be used with lava underneath.