The Dancing Princesses

A king who is extremely overprotective locks his six daughters in their room each night. But for some reason they order shoes from the cobbler practically every day and the king has to pay for them. And when he asks them why, they don't give him a straight answer. So he sends word that whoever figures out why they need so many shoes, he will have the hand of the daughter of his choice. But so far none have succeeded because they make sure no one can find out. But upon learning of this a soldier decides to find out after being given a cloak that makes him invisible.