Lightkey pointed out that we never mentioned this, so uh, here it is now! The map sources (BSP structure to mess around with in a level editor) to Quake 1 were released by John Romero last year under the GPL for the game’s 10th anniversary. GtkRadiant can edit Quake 1 maps, although I’m not certain how to go about doing that with the current SVN codebase.
They have been converted for yesterdays OpenArena 0.7.0 release together with self-made textures.
Download: [ 3ddownloads.com ]