Fish Tank Cake

I was inspired by Parenting.com to make this cake for my daughter's "Under the Sea" themed birthday party. It looked fairly easy, and since I worked the night before the party, I needed a cake that was fairly simple. I made this Homemade Funfetti recipe - only I doubled it for a 9x13 cake pan and baked for about 35 minutes. Because nothing says kid's birthday like Funfetti!

The rest of the cake was done the day of the party - it took me less than an hour for sure.
I frosted it with my Buttercream Recipe. Once I was sure the cake was covered evenly, I kind of swirrled the frosting, to make it look like water.
Sand = Heath crumbs (you can find it near the chocolate chips in the baking aisle).
Castle = Graham Crackers, cut to whatever shape you want
Fish  = Goldfish crackers and Swedish Fish. The bubbles are white frosting and the eyes are melted chocolate (although if I did this again, I would skip the eyes...).
Twisted seaweed  = spearmint gum rolled on a sugared surface then twisted. (I actually misread the instructions, it called for actual spearmint leaves... oh well, the gum worked great too).
Spikey seaweed = Jolly Rancher Chews that you microwave for 3-4 seconds then roll out and cut to shape.