Trying to randomly hit it with any magic is a *horrible* idea, 500 square miles is a ridiculous area for any magic. Besides PC has already said he deosn't want to use the "this half or that half" technique, I dont think he'll go for any variations of that. Too anti-climatic, methinks, and certainly takes too long.
Stupid birds hitting invisible towers? How about a permanent antipathy (avians) effect over tower? There goes the pigions and vultures. Not that there were likely many in the first place.
Still, that is at best a 17th level technique, but its an entire permanently invisible tower... waitaminute, just how strong *is* your opposition? It seems that the tower was developed by near epic magic, or loads and loads of permanency.
I'm thinking of some questions here:
a) Are the founders are still around, by way of being elves, undead or using longevity magics?
b) If not, how powerful are the current residents? 500 years of isolation and security, can result in weaker "decendant" spellcasters with a false sense of security. Thats assuming mostly humans and half elves though.
c) Weak spellcasters may lack certain defenses, and overconfident ones may make stupid mistakes. And who's to repair a broken enchantment? Dont know exactly how this might help, but keep it in mind, don't be afraid to try otherwise obvious or "lesser" approaches.
d) If it's not completely closed off, through teleportation magics, then you shouldn't be focusing on the location of the tower but looking for someone who knows how to get there. And of course, delivery people and mailmen are always a security risk.
e) If it IS closed off and it IS the original creators and they ARE high level, WHY ARE YOU GOING THERE???
f) Have any leads or wierd clues? Your DM may have already given you the key to an otherwise impossible task. It's an evil DM trick, I know I've used it.
