Cellars should have walls.
The whole concept also relies on FoV( Field of Vision) properly working. "Can't see into that house unless a window is open or you are inside of it", "There is no light in this house without windows or candles", "You cannot see into this cellar without breaking it's wall or being inside of it", "You cannot see outside of this cellar if you are inside of it, and all 4 walls are in tact".
Cellars should continually dig down deeper as cellars IMO, not simply some weird mix of cellars and mineholes.
I can't see this working too well with the way things are now, but with some planning it could happen.
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