Huge mounds and towers of clay, topped with gravel. The surface of this place is lifeless. Players can only see about 45 blocks around, because The Rigid is very foggy. Every now and then a player will stumble across a small opening to a cave. In the cave is all the life in The Rigid. There are larger cave than most in the overworld. There are under ground villages in these caves. In the chests in the villages are mine resources, adding onto the underground theme. Live stock are held in the larger caves, and most hostile mobs are on the surface. With The Rigid a new mob will be made, The Loner. The Loner is a mix of a hostile mob and a villager. You can trade rare items with it, but if players hang around it too long it will attack. Light in the cave villages will come from a new block called Riefer a glowing block that attracts bats.
Please consider voting. I bet this will be a fun update.