Cave Coins Plus was a medium difficulty stamp in Club Penguin, only available to be obtained by members. To obtain it, you must find the hidden coins in level 4 of the cave levels in Puffle Rescue.
How to Obtain
Near where the second pink puffle is rescued, there is a small arrow pointing to the right. While standing on the arrow, you must take five steps right, six up, and six left. You will then reach a platform with the coin bag, and a teleporter back to start.
This stamp was released on August 30th, 2010, along with the other Puffle Rescue stamps.