I once bought the DVD version of UT2004 to learn how to make virtual environments to design churches and monasteries. However, lack of intuitiveness in the editor, my not willing to sit down and learn it, and intrest in the game itself caused me to quickly abandon that.
How cool is this? These guys took a video game engine and made a virtual copy of the Basilica of Saint Francis in Assisi.
I did notice that they are missing all the choir stalls that go along the entire back wall of the apse. Still, the project is pretty impressive. I noticed that since they labelled it "1.0" it looks like they plan on refining it in the future. I'd love to get my paws on this.
For comparison, here's the only picture I could squeeze off.
You can purchase their program which gives you the ability to move wherever you want. I couldn't get the demo to work since I don't have the right operating system.
More info here:
Institute of Digital Theology