Putting the pieces together I wanted to go with a small mining town feeling that probably be the most common placed sites seen the fire location and that large cities would either be scares or built like a tower. Keeping that in mind I scattered Crystals about the place to indicate to the player this player was rich in the resource.
I later decided to change the sea to be a lake of Lava to try and give a better mood for the fire location. I added a portal to the location.
I added a portal to the fire location feeling that it be much shorter in range compared to the ones in the air ones due to it being man made, these portals only transported you across lakes of lava.
I felt that the very rock they'd walk on would be far too hot, even for the metal houses, so at the base of each structure I added a faint yellow glow indicating they were slowly melting, the black pipes supply coolant to the buildings so that the occupants would not roast inside.
Texture used-
http://shadowh3.deviantart.com/art/Rock-73682101
http://wojtar-stock.deviantart.com/art/metal-texture-5-60838049