Here's my Dwarf Outpost. I originally started building a tower out of pink insulating foam and kept adding and adding until this piece took shape. 90% of this piece is nothing but insulating foam and paint. I added the moss to the walls to give it an older look and made sure the walls looked like the had taken a few hits from stonethrowers etc. The last thing I added to the fort was the face on the wall. I felt the fort was lacking something that made it a Dwarf outpost so I added the face and I think it really made the whole piece come alive. I'll add a few progression photos as soon as I can find them!
Couple more photos showing details and add-ons.