One game I can recommend to you -
Arx Fatalis.
It's pretty similar to Ultima Underworld series, it's even said to be an unofficial successor to the series. It's also taking place underground, you're using runestones to cast magic, the entire feeling is there. Unfortunately, just like the Ultima Underworld games, it's also a bit too short and is finished before you notice it. Also there's no music unlike in UUW games, which makes for a bit more gloomy mood.
There's also
System Shock, from the same company, Origin. It's not a fantasy RPG like UUW though but more of an Adventure / Action / Horror mix, but very to recommend. Once you try it out you'll surely love it.