[color=green]You don't just kill things. You get to take their stuff! That's how the game works. It's how the story goes. Whence killed, the faerie's essence is recycled into a new creature. The dungeons continue on and on endlessly forever.
If you are looking for things that are of Magic, and Ancient, then there are a few options. There is an ancient dragon or two that wanders around the caverns. Some ogres have taken over caves at the west end of the valley. They are magic, not ancient, but those caves are stable and consistant. They don't shift and change behind you like these do.
Or I can direct you to the Troglodytes. They are faerie, but they are resonant of an ancient past. Very ancient.