I found a how-to video HERE...
This cake was so much fun and easy to make! Here is what I used for mine:
-2 White Cake Mixes (each made by adding 1/4 c inst. vanilla pudding, 1 1/4 c milk, 1/2 c veg. oil, 4 eggs, and a tsp of vanilla) and baked in 9x13 pans
-2 Boxes (4 serving size) Berry Blue Jell-O + 2 c boiling water
-Food Coloring (opt.)
-Candy, Polly Pocket dolls, Paper umbrellas, wafer cookies, etc.
I did some things differently than the lady on the video...
I baked my cakes ahead of time and froze them overnight. I layered 2 cakes on top of one another. I tried and failed the first time with the "quick set" ice method for the jello. My advice is to let the jello cool to room temp, then poor into cake pool and refrigerate. I tinted the frosting a light gray color for around the pool. Polly Pockets are a perfect fit for this cake!