Trust your eyes... its cel-shading in Q3 on the whole map! Actually this is a very cheap method of cel-shading, but hey it works !
How is it done you ask? Well, cel-shaded maps are supported by  Q3MAP2 , a third-party Q3 BSP compiler that actually supports pretty neat features. I think this tool just generates insane small texturecoordiantes for the usual faces and then doubles them. The clones then get shaded with a special cel-shader that looks this way:

textures/cel/ink
{
qer_editorimage gfx/colors/black.tga
q3map_notjunc
q3map_nonplanar
q3map_bounce 0.0
q3map_shadeangle 120
q3map_texturesize 1 1
q3map_invert
q3map_offset -2.0
 
surfaceparm nolightmap
surfaceparm trans
surfaceparm nonsolid
surfaceparm nomarks
 
deformVertexes wave 100 sin 2.0 0 0 0
cull back
 
{
map gfx/colors/black.tga
rgbGen identity
}
}

It just draws the backfaces, slightly scaled up, with a black texture. And voila! you have some black lines around your geometry.