The Fairy Tooth Castle is a sand sculpture delivered to your child by the "Tooth Fairy". When your child places a tooth under his or her pillow, you carefully pick it up at night, and then place an order with Fairy Tooth Castle.
In a few days, your child receives the sand castle along with a letter from the Tooth Fairy, explaining that the teeth are what makes the castles glitter and sparkle.
The Fairy Tooth Castle is the idea of Sarah Whitmer, who had made a practice of doing this for her grandchildren. She got so much joy listening to her grandkids describe the sandcastles and letters they got from the Tooth Fairy, that she decided to go global.