Trying to help here! "Guest" is quite correct. If it's been in a damp enough climate to cause this much mildew, this guitar could literally explode if not handled well. With all due respect to Open Mike, and i certainly do respect her, I suggest that you do NOT put it outside yet in the sunshine.

We're talking about dampness (water) here. The water has permiated everything, the wood, the cells, the glues, and everything.

The best suggestion I have is to wrap it in a clean and heavy cloth, perhaps a bedsheet, and place it in the rear of a seldon used closet. This hopefully will allow the moisture to slowly escape to wood pores and aclimate over time.

I wouldn't touch it for at least six months. Then, when you do finally open it up, look at what you've got. (I forgot to mention to loosen all the strings). You may have junk, or you may have something repairable.

Good luck, Bob(deckman)Nelson