Did a bit of searching (both in the Castille book and the net) and I can't seem to find a map of El Morro. I didn't ever remember one being in existence but thought maybe I was forgetting something. Sorry.
Now, about plot ideas. I am guessing you are planning on changing cannon? (after all, El Morro didn't fall). If so, then I have a couple of questions that, I think, may inspire you.
1. El Morro is 'The Wall' not only in a physical sense of stopping the Montaigne invasion. It also represents the heart of Castille. Many Castillians take solice from the fact that 'all is not lost, the wall is holding.' What would happen to them if the Wall goes down?
2. At this point Good King Sandoval is still an untested. The Inquisition is really responsible for this war beginning. So, what happens if it seems to the King that all is lost? Will he sue for peace or commit the whole country in a bid to regain the peninsula? And what about the Inquisition. Possibly losing Vatacine City to the heretic, L'Empereur?
3. On the other side, What does this 'win' for L'Empereur mean to the unrest in Charouse and elsewhere? Will his vengence upon the Inquisition and their lackeys (as he sees Castille) sate his appetite for destruction or will it merely serve to cement in his mind that he is deserving of everything that is given to him. Alternately, what if, true to form this win means as little as last week's fashion trends?
4. Moving on from that, Castille is now won, and without Montegue's help. Worse, he is still mired in a war he simply cannot win, making no progress (assuming the heroes don't show up with a message from his wife...). How does L'Empereur now feel about this upstart who didn't win the first war he was asked to fight and now wastes untold soleils in far off Ussura while not gaining ground?
That's what occured to me just now.
Mark