I spent the other evening scribing the foamcard on the outside of the walls to resemble courses of stonework. When you're making six feet of the stuff, it takes forever. I've added a little chipping to the surface so far, and pressed a couple of blocks in as though they were slightly misaligned or the wrong size, but the main thing since then has been applying 2mm foam to the back of the walls. Once that's dry, I shall scribe it. Then I just need to thicken up the battlements and add flagstones, and I can finally get to texturing and painting.