I just learned about
Underworld Adventures, an open source engine recreation project for
Ultima Underworld which seems to be quite obscure for some reason. It was indefinitely suspended in 2007 but a quick check suggests that the latest build is quite functional. It supports both the full version and the
demo. The project also includes a high-quality music pack.
Some screenshots:
![Image](http://uwadv.sourceforge.net/shots/shot2.jpg)