Shiver Snowfield is three paths in the Shiver Region linking together Shiver City, Shiver Mountain, and Starborn Valley. In Paper Mario, Mario needs to travel through here to eventually get to the Crystal Palace. A long line of snowmen in the center path gaurds the secret door into Shiver Mountain, the items needed to open the door are in the city and valley.
The path near the valley has Frost Piranha's, and after you beat the chapter Gulpit's inhabit the path near the city. Koopa Jr. makes an appearance on that path.