The following is a seven-part tutorial series on using Blender 3D to make game levels using the *.map format (MAP) that can be exported and opened for further editing and compiling to BSP in GtkRadiant or other brush volume based editor.
Download: KatsBits – Map Source (c. 10 MB | *.blend, *.map, *.obj, *.mtl, *.jpg,).
Resources
– Blender Entity Helper Kit
– Blender 2.49 .map making
– Quake III Manual
– GtkRadiant download