It's Mai Castle

Mai works hard building a great sandcastle that she'd just like to protect it from getting wrecked. The boys think she's being a spoilsport; Oto and Vik just want to play something imaginative and fun. Thanks to Yoko's magic, Mai gets to have her castle all to herself - and it's life size. Very quickly, however, she begins to miss her friends. The only problem is, in their desperation to keep the castle safe, Yoko hasn't included a way in - or out. In the end, it'll take their combined imaginations to find a way out of Mai's castle.