This article titled "How To Grow Sprouted Onions" at Alternative Gardening talks about exactly that. I had no idea. All this time, if I didn't eat an onion in time, I would simply plant the whole thing as-is in the soil.
A stone castle almost as sturdy as its full-size counterpart for your yard or garden. Creative crafts lovers might be able to build their own castles; otherwise, check fairy garden specialty websites for intricate accessories such as this.