http://www-graphics.stanford.edu/~cek/rayshade/rayshade.html
Rayshade is a system for creating raytraced images, written in C. This site contains links on everything related to Rayshade, including the Rayshade FTP archives where the program itself can be located along with ports to various platforms, the Rayshade user's guide, the Rayshade quick-reference sheet, and sample rayshade images. There is much, much more, so set aside some time and get into the fast lane with raytracing online.