Thin Ice was a game located in the Arcade, where players must control a Black Puffle that is on fire through a maze covered in ice, melting as many ice squares as they possibly can along the way - while collecting items such as coin bags to earn additional coins. There are no lives, and levels can be skipped without completing them. There are 19 levels in total.
On level nineteen, there is a false wall that can be passed through in the top right corner of the maze. After navigating through this false wall towards the button (the block with a circle inside), the walls disappear revealing a secret room containing a coin bag for each level you completed.
↑"Thin ice is hard to find anywhere in Club Penguin. But the Lounge will be full of it Tuesday Dec. 19th as penguins turn mazes of ice into puddles of water in the new game." — Club Penguin Times, issue #61.