Using the rock-climbing theme, we found an action figure of Tori Allen, who is, apparently, a famous female climber. (This is not a sport I have any exposure to.) The idea is to pose the doll on top of the cake as if she's climbing, and then put small candies to be handholds and footholds. I talked the niece into the brownie instead of cake so we didn't have to worry about the doll sinking into the cake.
So, we picked out a turtle brownie mix and baked it in a 13x9 inch pan. Made sour cream ganache with good bittersweet chocolate to use as frosting (yes, I'm planning to have a piece of this, why do you ask?) and frosted it. Tomorrow before the party we'll do the decorating: put the doll on top, add candy handholds, some Twizzler strands for climbing rope, etc. The doll comes with a climbing rope, but I figure while the doll itself can be washed, the rope might not survive contact with ganache.