I just picked up the game after a long time away, and thought up an idea of what I would think would be a really cool mod and one that I haven't seen. If I had any modding skills/more time I would do it myself, but I figured I'd put this up and see if anyone would be interested in making it.

My idea is to add impassible/near impassible walls onto forts/strongholds. I always thought that forts never really lived up to their full potential because a lot of the time armies would walk around them.

So in essence I imagine it would work as a researchable tech that works like terraforming, but creates a wall (maybe a re textured mountain) that can only be made to an adjacent fort. That way if placed strategically between mountains or narrow underground pass, it can actually be used defencelessly and prevent armies from just marching past a fort.

Not sure how difficult something like that would be to implement, but I figured I'd put it out there.