Arx Fatalis (Arkane Studios, 2002) is among my favourite games of the last decade. There are numerous favourable comparisons to make between it and Ultima Underworld (Blue Sky Productions, 1992), mostly because it was intended to be Ultima Underworld 3, but the developers could not obtain an appropriate license for the name.
The game takes place in (or rather under) a fantasy world whose Sun has failed. As the Sun dimmed and the world got colder, various species banded together to build vast, underground complexes, to be their new homes. The truce between races didn’t really last once everyone got settled in, however.