Upon defeating the Frost Legion, a white-coloured door will open up somewhere on the snow biome. The door will be held in place by an unbreakable block above and below it, and when you open the door, you will be teleported into a new world with the text "You feel a blinding cold rush of air and when you open your eyes, you find yourself in an unfamiliar environment."
The new world you spawn in will simply be made up entirely of Snow Brick Walls and Snow Bricks and will look like an oversized dungeon. Upon arrival in the world, Frosty, a new boss, will spawn.
Frosty, who is the size of the height of the dungeon, spawns in the entrance to the cave and closes in on you. You are basically running back through the dungeon as you fight him as he knocks you backward much like the Wall of Flesh and crushes you against walls with OHKO damages. He attacks by throwing oversized snowball chunks at you which do 20 damage and inflict "slowed". The main problem with this attack is not the damage but the fact that you can't run as fast and Frosty does 80 damage when you touch him.
Frosty slowly shrinks as he is being chased, splitting into variations from the Frost Legion, much like the King Slime splits into smaller slimes. He has 60,000 health and by the time he is down to his last health, he is around the size of the player.
Upon death, Frosty drops 1 platinum and 10 Greater Healing Potions. Much like Skeletron, he is not meant to be killed for loot but to gain entrance to the cave.
The cave's ceiling is filled with Icicles, which are cut down much like Trees. They give 6-10 Ice Shards when they are destroyed. They deal 10 damage on impact and damage friend and foe alike, with the exception of snow-biome related enemies.
As mentioned above, the general shape of the cave is much like the Dungeon except much bigger. Large Ice Blocks can be found around on the floor like chests. Boulder traps and dart traps are found regularly as well.
The entire cave system is regularly lighted up by White Torches.
A recoloured version of the Wraith (this one is very light-blue), this monster follows the basic Wraith AI. When you touch it, your health quickly falls, regardless of your armour. This enemy does not deal any knockback and does not let the player enter invincibility mode. Upon death, it has a small (10%) chance to drop the Stone-Cold Soul.
A recoloured version of the Demon Eye, this enemy follows the basic Demon Eye AI. It deals 50 damage with a large amount of knockback when you touch it. Upon death, it drops 5-10 Glass.
You can find him here too. No information needed.
A recoloured version of the Slime. This slime does not jump like other slimes (It's too heavy). Instead, it slides around with little friction. It deals 50 damage upon impact and drops gel.
A recoloured version of the Bat, this enemy follows the basic Bat AI except that it moves two times faster. It does 60 damage upon impact and drops the Frozen Spark (50%) upon death.
Crafted from 10-20 Icicle Shards at a Table and Workbench, this item, when placed, turns into the Icicle found on walls.
Crafted from two Stone-Cold Souls, twenty snow blocks, one diamond, one Illegal Gun Parts and twenty Iron, this weapon uses snow blocks for ammo. Like the Crystal Bullet, the snow blocks shatter after hitting a surface, inflicting "Slowed". The weapon does 40 damage.
Crafted with one grenade and one Icicle, this weapon acts like a grenade except that it has a much larger radius and inflicts the "bleeding" debuff on impact.
Crafted with one Spear and one Icicle at an anvil, the Ice Spear is thrown like the Throwing Knife, but with a much larger range and it pierces anything in it's way. It can only be picked up by the player who threw it.
Crafted with ten souls of light, night, sight, might, fright, the Stone-cold soul, one of each gem, one Night's Edge and twenty Frozen Sparks, this weapon is HUGE and is swung in a full circle. It does fifty damage (Not very much) but turns any block within a 3x3 radius of your mouse into the non-corrupted or non-hallowed type. Each block takes 5 mana to transform. The ultimate cleansing method.
Crafted from one Explosives (item) and one Frozen Spark, this item functions like the Explosive in that it explodes when activated with wires. However, instead of dealing damage and removing blocks, this "explosion" is white in colour and will stop anything which it is in its radius to freeze. Blocks will be turned into snow blocks and enemies (and players in PvP mode) will not be able to move for five seconds, though they will not receive knockback.