No updates to look at tonight, it's too late. As the walls align to the floor on the left (V) and bottom (H) I've moved most of the offenders over and down by 1 map unit respectively by using co-ordinates - got to love them, they make perfect placement easy! If you've not done it before it's pretty easy. Click in the coordinates bar, top left of status bar and make sure it relative, i.e. @T. Then select what you want to move, hit D for Do it (or right click and select Do It). The command prompt will ask you to select a point to move from or you can enter the co-ordinates. Type 0,0 and press ENTER. Enter your new co-ordinates; a negative value in the X co-ordinate (the 1st one) moves it horizontally to the left, a positive value to the right, a negative in the Y moves it down, positive up. Very simple. In this case I selected the walls and used a value 0f -1 and 0 for the appropriate axis, viola my walls exactly where I wanted them.

Still have to tidy up some corners and stuff but overall, really happy. The Pit is now in the centre of the room as it should be.

@Loopysue that's the technique I used, the colour just doesn't work for me!

I concur. That last example is on the money. I don't know if you've tried this Sue but on a map I did for the Design Mechanism's, Fioracitta, I took a parchment background and played around with the colourisation of it in Ps to get an effect similar to the green on your coast, perhaps something like that could be the default landmass? I'm sure it could be replicated in GIMP or Affinity photo.

Here is a link so you can see what I mean: https://www.cartographersguild.com/showthread.php?t=45178

Definitely not Spectrum Sue! That is the antithesis of Grimdark - without de-saturating it a lot. Is this for a commission?

You could try using the Ancient Realms or Dark Realms annual styles if you want colour. A B&W style on parchment would also probably work.

That is bloody brilliant, though I understood next to nothing of the process...