|Here is the finished rock. You can see the clam cup at the front door of the Starbucks cup cave. These are great for new clams, because they won't fall out. This Starbucks cup cave does not have legs, but you can make yours with legs if you want to.
Notice the overhanging ledge that is on both sides of the cave. By the time your Starbucks cup cave is cured in fresh water the paper cup will be gone. This makes a great space for good bacteria to live.