So, I liked the natural forces/domains of air, fire, water and earth. It resonates with things like electricity, ancient ruins with even more ancient ruins underneath, underground redoubts, the Bible being accurate about lost cities now being discovered - you know anthropological accuracy of descriptions as well as the talk of even more ancient ruins of civilizations that were older than 12,000 years but lost.

So there is a lot of underpinning to 'old' things with magic powers or use of harmonics, light, harnessing of natural forces and so on.

I've always liked spells. I used to use documents (like contracts, laws and precedents) to precisely word binding spells on other parties. Calling on wind or fire to focus or create a condition if cleverly used would be fascinating. Objects of power.