Next step is to use thinned down wall filler and cover all of the exposed foam, cut out 3 cardboard doors to stick in the openings, fill the corners with bigger stones and debris, give everything another coating with thinned down wall filler and sand/rubble the base.
After reviewing several of the Terrain Tutors videos on building foamboard ruins (an ongoing tutorial project): Foamboard buildings
I went for something big straight away to see how I would handle that many cuts and if the template I made actually worked. I'm pleased to say that it did. I had a base idea but most I just made up as I went along. Maybe it shows. I did undersestimate the amount of work all this cutting and glueing is for just one object. Granted, 4 of these tied together would make great centerpieces with some smaller, lower ones surrounding them, and in theory, if I keep off the net, building 1 of these in a week should be doable, and painting it in the weekend. Since I have my template, I can make sure all of the follow on pieces will fit with this one.
I'm completely ignoring Frostgrave atm though, and I have a ton of stuff to paint for that as well! Oops!