I got interested in 3D computer graphics when I was 15 or so (don't ask me why, I think I saw a CAD demo of some kind). A few Nearly 30 years ago, I started writing a ray tracer, just for fun. This project has grown quite a lot since then.
A while Ages ago, I was experimenting with path tracing features (a la Kajiya's SIGGRAPH '86 paper). The image above (which is a link to a larger image in TIFF format, gamma-corrected for gamma=2.0) gives a hint of the power of path tracing. Note the penumbrae, and the colour-bleeding from the red wall onto the box. Now I just hope noone at Cornell sues me for stealing their test scene geometry :-)
Today, the program has support for most of the RenderMan interface, including the shading language, and can render several example scenes from the BMRT toolkit. However, I haven't touched the code at all for nearly two 20 years, for lack of time and inspiration.