These decorative forges are obtained by going to the
Primeval Lich champ spawn. They are for decoration only and have
no other functionality.
I love the idea of the normal one either above or below while the single tile one sits in your crafting area. Back before I quit in 2007 I had a broken one sitting on one corner of a Keep. I laid out an area of the square goza raise them then dropped the soul forge on them, when I lower a square, where the anvil was, it broke the forge. Never did that again as I had gotten the small soul forge later.