False wall

see Linedefs; a "false wall" is a "2S" (two-sided)linedef, with a middle texture, often with lower unpegged flag set, and Impassable flag OFF, an example of this is E1M1: Hangar if you are in the zig-zag room, you cannot look into the secret passage, however, if you are in this passage, you can look out. it is recommended that use a diffirent flat for the sector behind the linedef, if not, the Middle texture will "bleed" into the floor, or ceiling, or both, especially, if the sector is less than 128, and the texture is 128. the linedef can also have a texture on both sides.