Thanks for the feedback!
No problems with the bridge middles, but I will thoroughly test them again.
A ruined tower on the island has crossed my mind. Would go well with the ruined bridges.
I'll tweak the fort some, maybe try a different set because the "small_wall" for this castle's texture is not small at all, or even shaped right, so I cannot easily add cover to the stairs and walkways.
Invisible walls aren't usually an issue unless you're cavalry and get drawn away from the central area. But since I hope for this to be a cav friendly map it's a concern to me.
I've used the smooth tool often, but I do see some places that need it, especially the shorelines.
Thranduil, I like your Sky Castle, reminds me of the PC game Stratosphere.