How about I add a small wooded island to the middle of Feather Lake... about 6 miles in diameter. Fortress as you described in the middle of it all. That works for me... you'll want forbiddance, of course.For my stronghold, could it be an enormous oak tree rising out of a moat-like lake in the middle of a forest? Preferably with rooms in the tree (warp wood created or such, so as not to harm the tree) and rooms outside, along the trunk and branches. Iono too much about the rest of the specifics, probably whatever you think would be good.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.