Ok, bit of an idea I have for your mod. Underground villages for the remaining Gelidusians.
On the surface you will just see a broken tower however when inside you will see a staircase down. These open into a large space.
The space itself is a sphere with the bottom third filled in. In the center of the floor is a large open lava pool providing the vital heat to the inhabitants. The Entrance opens in to one side of this space.
Along with the floor there is a second terrace at the widest part of this space that goes around the outside of the space. Up at the top third there is another walkway around the outside. All 3 walkways are connected by stairs.
Now this is just the infrastructure. Opening into these walkways and build into the side of the hollow are the buildings.
Small den: A small cave with a table, torch and chair. 2 by 3 space inside with rough walls.
Medium den: A 3 by 3 den with a better floor, walls and ceiling on top of the stuff in the small den.
Large den: A large den with wooden beams on the ceiling, a wood floor and good ceilings/ walls and a netherack fireplace.
Mushroom farm: Really rough caverns where mushrooms, or whatever is eaten in this dimension, is grown.
Storeroom: Large structures where any valuables are stored. These areas are guarded with ferocity. Only one spawns.
Inns: Only one spawns. These 2 story structures have a bar area in the bottom and a few rooms in the top.
Markets: Large open structures where Gelidusian traders stay. Here you can trade for materials.
So, that's my idea for a town in your ice dimension. To add to the theme you could have occasional caravans of Gelidusians wandering the ice wastes. Gathering materials and trading between the hollows.