id Software, the maker of the Quake and Doom series of games, has always been a pioneer of real-time computer graphics. In 2001 I built a small tool to render level files from Quake III Arena, complete with support for curved surfaces, lightmaps, textures, skies, collision detection, visibility determination, and animated entities.
I later updated this tool after the release of Doom 3 to support its map and proc world file formats. Unlike the Quake III format, Doom 3 used plain text formats for its level data, which made the process of decoding the layout much easier.
Although simple, this tool also offers a few additional conveniences such as key binding support and console input.
Note this demo is not packaged with any world files (as they are protected under copyrights by id Software). If you do not own Quake III or Doom 3, you can download the Quake III Arena demo to obtain the sample maps. Additional instructions can be found in the documentation that accompanies the id World Viewer software.