He wrote a whole article series walking you through it, plus source, etc, starting here: http://www.shamusyoung.com/twentysidedtale/?p=2940
He released the executable at the end of the series, and I'm still sad that, as a non-programmer, I couldn't get it to run on my computer. I would have loved to have a chance to explore the world. Some of his screencaps are mindblowing.
[ETA: Since it's not immediately obvious how to get there from the rest of the articles on Project Frontier, here's the link to the source code: http://www.shamusyoung.com/twentysidedtale/?p=15808]