A quick question - I have been participating in a different thread, want to have all my bases covered before I dive into Ultima Underworld, and another question came to mind. I know in some other RPGs, the player can earn experience points through both combat (melee) and/or through successfully casting spells. Other RPGs are not like that - the player can earn experience points through defeating enemies outright. Which of these two applies to Ultima Underworld?

You gain XP by defeating enemies and exploring (every new bit of map unveiled provides a bit of XP, and this is actually a significant source of XP throughout the game). Individual weapon swings and spell casts don't matter.

When you level up you get training points, which you spend at an ankh to improve skills.

Note that there is no call for exterminating everything that moves. There is enough exp from hostiles/exploration to get you to max level without trying to butcher all of the neutral or friendly creatures in the game.