Making a false wall

A simple trick used for creating non-solid walls (often used for hiding secrets) as well as making gates/fences.

Create a sector and make another sector connect with it. Highlight the linedef in between the sectors. Open up the sidedef textures menu and put the texture you want to use in the middle texture slot. If you intend to use the linedef as a solid gate, make it impassable via the linedef menu.