Build a fortress to withstand almost anything

[Ghostwind]

These are some great suggestions. I should add that I am also working up a version that fits high magic and uses protectively spells freely, but I wanted the lower magic version so it could be dropped into any setting and be difficult to breach. As soon as I get stuck on it, I'll make a new thread for help on it.

 

[snarfoogle]

High magic, eh? Develop an epic spell which creates a moving bubble of force which allows air to flow through. Place gigantic castle inside. Develop epic level shrinking spell. Develop epic level pass-through-rock spell. Have 100 foot diameter bubble float through the planet's crust and oceans.