The Brothers Grimm 
The Twelve Dancing Princesses 

In this tale, twelve princesses, each of astounding beauty, are locked in their shared bedroom by their father each night. Vexed to discover that their dancing shoes show signs of wear every morning, the king demands an explanation, which they refuse to give. The king offers his kingdom and marriage to any of his daughters as a reward to the man who solves the mystery. However, if the mystery remains unsolved after three nights, the erstwhile suitor will be put to death. After many entrants fail, a wise old soldier finally cracks the case.