Over the years, Club Penguin has created several hidden rooms to explore. The most obvious one is the Iceberg, visible on the far right side of the CP map. Mouse over it and you can see you are able to click on the iceberg and go there.
It has long been tradition on CP for penguins to congregate on the Iceberg and drill (using the hardhat item), trying to tip the chunk of ice.
Next, there’s the undersea room, which you get to through the Hidden Lake, using the sliding door on the far right.
The Underwater is the only room in CP completely submerged in the ocean.
Finally, we have the Box Dimension, originally released during the 2009 April Fool’s party. Orange puffles can be seen floating through the room, and Rockhopper once stored plants there. Snowballs bounce when they are thrown in the Box Dimension. To enter the Box Dimension, look for a box in the bottom right of the Lodge Attic. Mousing over the box reveals a swirling purple vortex: the gateway to the Box Dimension!
You can also use the Box Dimension portal item in your or someone else’s igloo:
Have fun exploring CP’s hidden rooms!