This will be my first official post on the wonderfully interesting-to-read TaleWorlds Forums, so please, be gentle.
First and foremost, I am not entirely sure I've seen this idea expressed yet whilst perusing these forums; if I am repeating an already-discussed topic, please do quote or correct me and I would be delighted to read it over! Thank you!
I'd love to see buildable castles/forts/hideouts/garrisons on the map. I used to revel at the sight of a vast enemy army failing hopelessly at sieging my castle atop a mountainside or upon a large hill... Watching arrows whiz by in arcs of deadly shadow... truly an immersive feeling. Despite knowing there may be coding or physical limitations of how and/or where we could "build", "design", and "place" these fortifiable buildings, I most certainly would find many ways to take advantage of the natural terrain of Calradia. They could be like the text-based upgrades you could make to your owned villages, castles, and towns - but instead of being lost if your enemies the territory through pillaging,
Imagine a constantly adapting world where your friends and enemies alike can expand and conquer in a simple but intrinsic way every time you play...
Example:
Got a despicable neighbouring faction with low morals or a nearby bandit settlement that loves to encroach on your lands and pillage? Sick of everyone murdering your defenseless peasants out in the open plains the moment they leave their home area?
Solution:
Start building up proper defensive lines. Be a wise Vassal/Lord or Lady/King or Queen and PLAN out a tactical patrol with a reasonably easy-to-defend route. Let's use all that taxpayer's money to build a fancy-schmancy new fort/base to where troops can be sent directly to constantly patrol the region. The result is pure profit. Save countless innocent lives. Reinforce your claim to an area. Intimidate your enemies and reestablish trust with your people.
This would not only boost your faction's/kingdom's overall morale and economy, but also display an understanding of the need to protect your loyal citizens from harm. Perhaps these forts could be built as part of a quest given once you become a lord or perhaps you've just inherited your family's lands? Could this type of thing have an effect on your personal, immersive story later on? Save a village from imminent death, perhaps a few weeks later they show up looking for you, and offer goods or service to you/your faction! More troop recruitment from that village? Maybe they offer to work for you and pay you more taxes for the added safety it brings them weekly/bi-weekly/monthly!? Add a weekly bonus relationship with the surrounding villages/towns affected by your shrewd use of the terrain!
I'd love to hear everyone's thoughts and opinions on it!

I want to know if it's even possible, and if so, is this a good idea at all?
TL;DR Basically I want to be able to have custom-placed forts like the Bandit Camps that could spawn in M&B: Warband, and have quest-related or lore-based reactions/rewards for protecting villages or cutting off enemies by using a defensible castle on a natural mountain path; perhaps a rocky ledge to build a fort and fill it with archers/crossbows... et cetera