I don't often remember where I was when I came up with a particular puzzle idea. In this case, I have clear recollection. I was in the Mickey & Friends parking structure at Disneyland. Realizing that ELF ON THE SHELF was amenable to a symmetric layout with both ELFs placeable on "shelves" was the key insight driving the puzzle's creation. It was a bit challenging to find a block layout that worked without creating any pseudoshelves, but I'm pleased with how everything came together in the end. Happy Holidays!