3dfloors.wad 
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Effect demonstrated: - 3D Floors
a) Make a dummy sector. (A dummy sector is just a little sector not connected to anything else in case you were wondering).
This dummy sector will have most of the properties of the 3D floor. It's floor and ceiling textures control those on the extrafloor. The lighting level (and blink effects) control those underneath the extrafloor.
Give it a distance between floor and ceiling of the thickness you want the 3d floor to be: by this I mean that the floor height of the dummy sector will be the bottom of the extrafloor, and the ceiling height will be the top.
One of the lines of this dummy sector should be 400(edge extrafloor). Give this line a tag number(for example 106).The texture on the tagged line in the dummy sector will appear on the side of the extrafloor.
b) Now place a sector where you want it to appear in the map and tag this sector to the line defined earlier(106)
This is the code for the Edge prefab (if you're interested):
[400] // EDGE Thick Extrafloor (dummy texture)
TYPE=PUSH;
ACTIVATORS=PLAYER;
AUTO=TRUE;
EXTRAFLOOR_TYPE=THICK;
