I checked out there’s a exclusive sneak peek of the new room in the mine (Door)! You can see it from the Club Penguin Times Issue #223 & #222! Check it out here:
Also i found a sneek peek if it might be a under water cave:

It’s soo cool!!! Wow!!!! I can’t wait until Friday! That we can go for the adventure in the new room! Wohoo!! Whoot Whoot!

Until Then…Waddle On!