Ice Caves are structures that spawn randomly underground in cold (snow) biomes. It is a rather complicated tunnel complex, with a floor made out of ice. The tunnels contain Goblin spawners, which stand on top of chests, containing the typical Better Dungeons loot.
The boss mob for this structure is the Ice Bull, a dark blue and strong looking mob, resembling a cow. It has 300 HP, and uses a very fast charging attack, which deals a considerable amount of damage and knockback. When charging, the bull destroys any blocks that are in his way, except bedrock. The bull can turn air blocks in the floor into ice, so it is impossible to make it fall down.