The Twilight Glacier is a biome added by the Twilight Forest mod. This is the only biome that Penguins spawn naturally inside of. The Twilight Glacier is a tall biome made entirely of Ice, though it can be changed to Packed Ice in the configuration file, and it is one of the tallest biomes within the Twilight Forest mod. It is typically in the middle of a Snowy Forest biome. The Twilight Glacier can only be found in the Twilight Forest dimension. Aurora Palaces are commonly found in these biomes.
If the player hasn't killed the Alpha Yeti and they attempt to walk in this biome, they will be slowed down significantly. If they find an Aurora Palace during this time, the Snow Queen will be invulnerable to damage while the Progression Shield is active.